You've got to make Olimar miss, thats the place to start.
In a theoretical argument on paper, Olimar's range and move set allows him to beat all of MK's methods of approach, period.
Fortunately however, no one plays this game on paper
NC Echo offered neutral B, which is definitely the most difficult approach to deal with. What makes it so difficult to deal with? The limited options and precise windows of opportunity Olimar has to use in order to deal with it. So consider your move set, what your good at, what Olimar is bad at, and what Shrink is bad at. Your best options are obviously the ones that MK is good at but Olimar is bad at dealing with, layered even further by what parts of MK your good at and what parts of Olimar Shrink hasn't quite developed all the way. Olimar has limited options to deal with opponents coming in diagonally for instance, UpB. Does Shrink make good use of UpB, even in quick situations where you jumped from just outside his range, floated over the treacherous FSmash/grab potential hit boxes, then came in at 45 degrees with an attack in his face? Maybe you'll catch him flustered, or not thinking to immediately go to the UpB the moment you commit to that diagonal approach? Thats the kind of stuff that figuring out match ups comes down to, on paper creating difficult situations for your opponent, opportunities for him to make a mistake that allows you take advantage of the mistake.
No one is perfect or any where near it, same is true in brawl. Paper arguments only help you develop before and after a match, but all of it means nothing if you can't make use of it. MK isn't a character who makes his living by knowing the exact right counter to every possible situation, hes quick, he can improvise very well. You don't need to figure out specific approaches that you can practice and practice in hopes of perfecting. To approach better, and overall play better but most importantly in approach, you need to become familiar enough with MK and comfortable enough playing him that your no longer thinking about what buttons to press or worrying about timing and instead get creative, what can you do to force a mistake? Approach in ways that look deceptively open, encouraging an attack that maybe your opponent thinks is open, but you have the control and knowledge of MK that your sure you'll be fine, either with a roll or dodge or even because you just are spaced correctly outside of that moves range. You'll need to know if you roll towards if your going to have enough time to attack, or dodge again before you'll get hit, you'll need to know if you shield an attack whether you'll need to take 2 steps and then DSmash or can hit from where you are. This "supreme knowledge" of any character however is again, perfection, we've crept back a little too close, but hopefully see my point. If you know the game better than your opponent, and you can make use of it, you'll win any match up your familiar with.
So, back to reality with a simple example to take paper back to controller again. You can't hit Olimar before he hits you unless you force a miss, we've established this. The ways to make an opponent miss are not limited to the 6 or so simple approaches anyone could write down, no different here or on the MK forum. What does your opponent do when you start to dash at them, and then SH out of range as if to FAir, but instead, before your too far and can be hit, you DI back and land safely out of range again? Sure you didn't land a hit, but was the Olimar forced to guess an UpB to protect himself? Run in and take advantage of it. Or what if you actually just ran away from Olimar for a solid 25 seconds, with your jumps rolls gliding and dash speed this isn't really that hard a task. Is the Olimar so frustrated now though that they are trying far less safe tactics, desperate to hit you and stop the game of chase? Can you punish those attacks? Don't take this too literally, I'm not going to sit through shrink's videos if they are all 10 minutes because you run away for half of them, not to mention you probably will have trouble finding people willing to play against you. But do take the spectrum of this paragraph seriously, getting creative isn't just randomly mixing in a dash -> USmash to your normal routine of dash -> attack and dash -> grab routine.
Approaching has a distinct advantage, it pressures the opponent into making a correct action to deal with it. It also has a distinct disadvantage, the more your opponent sees a particular approach, the better they become at making a correct choice to it. Good approaches force difficult decisions that require great reaction time or prediction of which way you'll go in order to make the correct choice. If you fall into habits, good approaches become bad approaches because your opponent knows both what to do, and which move your going to try most the time. Doesn't matter if that move is an attack, a dodge, a jump, whatever, if your opponent knows whats coming how could they lose? So make use of all the options and do too many different things for your opponent to ever know whats coming.
-True