My 3DS XL is so old that the rubber bumpers were very hard to remove.

So I tried to heat the rubber bumpers a little bit with a hair dryer for 15-20 seconds, with some pauses every 5 seconds in order to avoid overheating or damaging something as a precaution.

It worked well to remove them but the only drawback is that as my rubber bumpers already got damaged and scratched because of my previous attempts without heating first, heating it up after aggravated the scratch damages when I used tweezers.

So I would recommend heating the rubber bumpers moderately first and be gentle when using something that could scratch or damage them.

(Do not take my words for it, it may not work for you)