Functions.php file vanished

Question

I've added a custom menu item to the functions.php in BuddyPress and it added a link 'item one' to the member's navigation template on this page

https://www.myequinemojo.com/members/indk/

However, when I came back to change the name to what I want it to display as, the entire functions.php file has disappeared from the plugin directory, so not only can I not edit it, I have no idea where to look for it?

Can anyone recommend a method of finding out where it could have gone?