themeforest purchase key login for BeThem, activation, and upgrading to php 7.2

I almost forget what i started trying to do.
I want to speed up our small wordpress physio clinic website.
i realized i should upgrade the php, from 5.6 to 7.2 is possible with our newish godaddy.
i checked compatibility with a plugin, but it timed out, so i looked into BeTheme forums(on envato/themeforest), but I need to create an identity using our purchase key to do it.
I took over this from the clinic’s co-owner who moved on, and I can’t find any purchase key info.
also, in the wordpress themes i have a blue button to activate BeTheme 17.8.1, from a (child) BeTheme 16.0.1… that we are currenty using i guess.

Can I recover a purchase key, finding nothing in old emails? if i purchase a new one, can I just paste that in? is there a reason the guy never activated BeTheme 17.8.1 or upgraded to php 7?

i am, clearly, a newb.