οὖν affixed to a relative pronoun has a generalizing force and makes it indefinite ( cross339 e). Such indefinite relative pronouns are construed like the indefinite τὶς or demonstratives; and do not introduce relative clauses (unlike whosoever, etc., which are both indefinite and relative).
So with adverbs ( cross346 c), as ὁπωσοῦν
a. Simply placed after relatives οὖν has a strengthening force; as ὥσπερ οὖν
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].