A pretty common problem. Agfa cameras are famous for frozen focus. Try the following:

Aireis cameras aren't all that common, but you might try a google to see if anyone has advice for your particular camera.

Sometimes the helical just won't come undone - I have repaired many a frozen Agfa, but I have one where 2 years of soaking in acetone/methanol/MEK/xylene/pure hasn't loosened it.