Decrypt footer.php ?

Hi, I’ve found a number of resources to decrypt an encrypted footer so that I can edit it a little but nothings I do seems to decrypt the footer. Probably because I’m new to this. I don’t want to remove the author of the theme, I would just like to add a few words

This is the link to the theme and I’d really like to keep using it:
https://wpclassic.com/tungstenation/

Any help would really be appreciated.