I am atm working on this issue, and it I’m afraid the ‘C’ drive is an SSD that is soldered on the motherboard SDINAF4-464 in my case. There are videos on YouTube that detail the steps for removal/ replacement of similar chips. However with the tools to do so and the learning curve… probably better to have done by an actual repair business. Look up ‘re-balling a chip’. two YouTubers of note; iPadrehab and Louis Rossman both.com.