Example -
If you or Theresa has time, let me know.
If you or Theresa have time, let me know.
Which one is correct?
Example -
If you or Theresa has time, let me know.
If you or Theresa have time, let me know.
Which one is correct?
The subject is singular - it's either Tom or Theresa. The verb form usually depends on the principle of proximity:
If you or Theresa has time ...
If Theresa or you have time ...
I believe, since you are addressing "you", then the 2nd person case would be correct.
If you have time, let me know. If you or Theresa have time, let me know.