Find & Replace Value of a Key in request Headers

Hi all! I have received a collection where the header for each request has a key:value and the value of that key has to change.

There are 946 requests to update. I was hoping Find Replace would work but I can’t figure out how to get it done. Or do I need to use something else?

This is what I need to change:

Current Headers

Change to:

Any assistance greatly appreciated!