This is one of R.O.B.'s problems, so it's totally normal to have trouble with this, btw
First of all you can use Nair to scare the opponent by throwing out a hitbox, but obviously that won't work every time. You can use Dair to stall your landing, but make sure to do this at a safe distance due to how long it takes to come out. Bair can alter your momentum but it's
really slow, though it's still an option to keep in mind. Then there's Up B, which will do practically nothing if you're falling down; you can use it when you're still being launched upwards and your opponent is trying to get a followup, or when you're at that point when you're not moving at all, but it's one of those niche options that also might use up your fuel.
Gyro Cancelling can also help (which you can see
here) if you B reverse or wavebounce while doing it. This is the safest option, but sometimes there's not really an opportunity to do it (also it's kinda hard to do, but it should be worth it).
Basically Nair or gyro cancel should be your go-to options, but the main thing to note is that you shouldn't take too long to get back to the stage, because that's just asking for a Uair.