Crashing file due to (mistakingly) edited backup

[Bob]

Hello Gnucash community,

I've been having problems with my Gnucash file. I think I mistakingly
edited one of the backup files and now I can no longer open my file.

I am presented by a prompt asking if I want to open it anyway, in which
case it ends up crashing (not sure if because of this edit or because of
40,000+ transactions that I wanted to delete).

It does open in read-only mode.

My question is what can I do to have a working copy?

I appreciate your help. Thank you

Regards,
Bob