Replace Specific Text(words) in a Post with Other Text(words)

If there is some text written in my post

For example:

by rahul gupta

Now I want to replace this text “by rahul gupta” with another text like “by mazakaro” on the runtime when ever post content is being get fetched from the database. I dont want to replace content from the database, I just want to replace at run time.

Please tell what change i have to make in wp-functions or some other file.

Thanks