Transferring a CPU/NAND combo to another logic board for data recovery, while possible, is THE MOST difficult micro-soldering repair to perform. Many experienced techs won’t even touch it. Not to mention that you need a functional secondary device (or logic board) in order to accomplish the data recovery.
So I’m afraid to say this is not something you can learn for doing a one-off repair. Your best bet is to find a shop that specializes in this kind of repair. If all a shop can point to is Tristar or iPhone 7 Audio IC repairs, then this is not the shop you need.