Postman: add a given header to all requests in the given collection or collection-level header

Your question may already have an answer on the community forum. Please search for related topics, and then read through the guidelines before creating a new topic.

Here’s an outline with best practices for making your inquiry.

My question:
Postman: add a given header to all requests in the given collection or collection-level header.

Details (like screenshots):
I have “x-apikey” header & a bunch of requests in the collection without this specific header.
How can I avoid manual work of adding header one by one to each request?
Anyone has an existing solution, please?

How I found the problem:
Imported OpenAPI spec & it does not contain the needed header. Hence, need to add to each request.

I’ve already tried:
StackOverflow