Guestbook and PHP 7

[Calvin39]

Can anyone give me any advice please.

I have a Guestbook and it is linked to our website and forum there are some  5,000,000 if not more entries World Wide.  I however am starting to realise that IPB Board is moving more and more to PHP 7 now my prediciment is this the guestbook will not work with PHP 7, and the writer of the software who did it for me has stopped working, and I can no longer contact him, I paid for the guestbook outright so the copyright is mine.

Is it simple to get it to work with version 7 PHP if not do you know of anyone who could fix it for me.

I really cannot afford to lose it under any circumstances, it really is a must have.

Any replies please in a 20 font please as I have very little vision left.

Thanks for any help Gerry