I'm trying to do a regexp with a replace.

I have the following regexp:
^(?s)(?:.*)(?:Resistance Z/F A-Pair TG\s*)(\w+)(?:.*)

On the following source examples.

Resistance Z/F A-Pair TG OR Kohms
Resistance Z/F A-Pair TG 1234 Kohms

The regexp currently returns the "OR" in example 1 and 1234 in exmplae 2, exactly what I wanted, however I need to change/replace the OR in example 1 to a zero (0).