The developer I was working with has died and I need someone to pick up and complete the project from the current state

This is a B2B software product. I have access to source code and DB side standard procedures and table structure (in excel). Tech stack is attached to the requirement.

Notes:
There is no documentation available explaining the code.
The code is not commented on
The code was working fine till a few months back but is not working presently

I am looking for someone who has experience in picking up from other developers' code.