First replace the hard drive:
https://www.youtube.com/watch?v=E6ktZ6PN2zg
Install Mac OS and get an external USB SATA drive case for your “damaged” drive.
Personally I would buy 2 extenal USB cases and 1 extra drive for the 2nd case. I would then do a complete clone copy of the damaged drive, in the first external case, to the 2nd drive in the 2nd external case.
Oh, and don’t buy those “name-branded” USB external drives. Buy 2 separate cases and one separate hard (for backup of “damaged” drive) at a PC computer store - much better price.
Otherwise you risk damaging all your important data.
Remember the data is most likely to all be there. The directory (or what ever Apple calls it) is corrupted, this is for sure.