how do I unlock weapons from For new returning users?>

When you came back after at least 30 days of not login game:
1. Choose weapon ( on welcome back window you can select some temporary items AND a proto weapon).
2. Login game for next 7 days.
3. Play at least 1 game / month for next 3 months.

If you fail at least one of those requirements the weapon will be removed from your storage.