Fatal error: There has been a critical error on this website.

Hello there I don’t know where or whom to be writing this to,

I recently bought the AUTEUR theme from a Recommendation for my online Bookshop, but after installing both of the Zip files from it, the, “g5plus-auteur-v5.4” and the “g5plus-auteur-child.zip” my site is unusable and unreadable and I don’t rightly know what the heck has happened or gone wrong, if anyone knows what has happened and what I need to do to get this error fixed please let me know

thank you