[Goatboy]

Was it just the blade or the whole wiper arm that came off? More that likely you will need a new wiper transmission (linkage under the cowl) if the splines for the arm are stripped. If not, you can try to grease the bushing on the transmission to see if that frees it up.

 

[Goatboy]

A pic would be more helpful but I'm guessing you're going to need the whole linkage assembly. I don't think the parts are sold individually.