One seed two cotyledons. What to do?

Cut the smaller one off, you can not pluck it out, it is attached to the bigger one. However, in my experience, twins have defective genes and don't flower properly.........I get rid of them as the risk of wasting a lot of time and effort is too high.

OO twins. pluck the small one out and grow it in a diffrent pot.

you've got a 'twin' of some sort. no idea if fraternal or identical. cut the smaller one. It will forever be behind in competition with the larger sibling. if it's fun for you, keep it, but for best results kill it. It shouldn't be a big hinderance, but it'll be in the way and leaching nutes away from the stronger one.