How do I fix my iPhone 13 after water damage?

From your description, it appears that your iPhone h.as sustained water damage and the logic board has been affected. I recommend that you contact 👉 Official Apple Support OR you can always get your iPhone examined at the Apple Store 👉 Genius Bar Reservation and Apple Support Options or at an Authorized Service Center for further diagnosis and evaluation.

Axel F

Water damage can't be repaired. Apple won't try to fix an iPhone which has been subjected to liquid intrusion. By all means have the phone checked by Apple, but the moment they see the water sensors activated, they'll either offer you an Out of Warranty replacement phone (same model for about 60% of the cost of the phone when new) or you'll need to buy a new iPhone.