so, the most important thing apparently is acceptance and optimism
the more and often you think about your tinnitus, the more you pay attention to it, the more you suffer and the louder it gets.
in my first month of tinnitus i could not spend 5 minutes without thinking about the noise and thinking about how i will suffer for the rest of my life but I found a great article explaining that I developed the "brain of attention" which leads to more and worse tinnitus so I tried my best to not think about it. it was hard at first, spending time with people, watching anime or playing guitar helped me to distract myself. I also noticed that some weed strains made the symptoms worse so I entirely quit smoking it. I made sure to always sleep 8 hours and if I couldn't fall asleep because of the noise i'd just not give a fuck and call in sick for work the next day. I also started to eat a bit more healthy food, but my diet has never been that bad anyway.
Now, 3 months later only at night if I pay attention I can notice a really little noise that is so quiet it doesn't bother me at all.
I also did a hearing test and I could still hear frequencies up to 18khz (i have always taken care of my ears so far) so my tinnitus was not caused by physical damage to my ears, it was something that could be solved by changing the way my brain acts and this is something you can learn.
TL;DR
Let your fren do a hearing test, if everything is okay, chances are good he can recover by himself.