Medical professionals are there to help you, and they have seen and been asked to do almost everything. This is a medical need, so you should not be concerned about asking, and it's good that you thought of doing so.
Just approach the situation as you would any other medical need. State that you are concerned about maintaining cleanliness, and that you don't have the dexterity to properly clean under your foreskin. Your sexuality should not even be a factor - your caregiver should be willing to do this whether you are gay or straight. If you keep it professional, just a you would any other need, you should be fine.
If it helps, I totally agree with CurfewX. Just ask it as you would any other medical need - professional, factual, and straightforward.
I also agree that your sexuality isn't a factor here. This is the same thing as cleaning behind your ears or your back, really.
Good for you for realizing this needs to be done. :)
Thank you guys so much! I just started adulting and navigating what I actually need. I really appreciate the advice and will use it the next time I see the nurse