How to activate offline donation version in windows by command line
If you do not have an active Internet connection, you cannot.
Having Donation, & having a valid key is not enough.
Still there is a (Internet based) check.
On the Internet-less end, you can generate a "request" that you can then "send" to FFS (from some other computer with Internet), that will then generate a further key (if I'm remembering correctly), that will then validate you (offline).
[Donation Edition] Activation - offline...
(My thread dealt with Portable, but from what you describe - without Internet, the same actually applies to the installer too.)