Use multiple find requests to do an OR search instead of an AND search. For example:
Enter Find Mode
Set Field [ Table2::field ; $value ]
New Record / Request
Set Field [ Table3::field ; $value ]
Since your criteria has been entered into a global field, there is no need to use a variable. Your set field steps can reference the value of a global field while in find mode.
For examples of that kind of find script, see this thread: Scripted Find Examples