As others have said, you need to use the finesteride indefinitely. This is a presciption approved drug to treat hairloss, there is only one other that I know of, which is Minoxidil(Regaine). You could use Minoxidil too, this needs to be taken indefinitely too.
Whether the Primo will be ok for your hair I don't know, but you certainly have a hell of a lot better chance than with tren
Tren is very androgenic, and the more androgenic an AAS is, the worse it is for your hair. Primo is at the opposite end of the scale in terms of androgenicity.