then how to restart it from that step after fixing the problem?
You cannot use RESTART directly to do what you want. As MrSpock mentioned, you probably have a lot of editing to do. You may also have dataset/database considerations.
Depending on the process, you might be ahead to restore everything to the starting point and completely re-run the job (once the problem has been corrected). If this is an actual production problem, i suspect that rerunning everything 2 days later will not work. . .
Suggest you review the process and remove the need to restart inside of any nested procs. Or just leave it as is and do the same amount of editing/preparation to rerun if it happens again. . .
With few exceptions for certain utility functions, sites i've supported to not permit nested procs.