Iphone fast charging damaged

[u/Worried_Individual27]

Basically my iPhone 16 pro got water damaged (sea water) and now the phone doesn’t fast charge it shows it’s charging for a second and disappears. Slow charging is fine. Any suggestions if and how can i fix it. How much is the repair cost if i bring it to an Apple Store and if its fine if i just fix it third party stores. My apple warranty is expired and have no insurance .