Recently working on XSS, I haven't used Burp's replace function for a long time, so I'm recording it. I used to use other tools for this.
proxy - options - match and replace
Add a rule:
^Cookie.*$
Cookie: cookie content
Pay attention to the colon in front of the Cookie content, do not use Chinese
After adding, check the enabled box, and every request passing through Burp will have a fixed cookie.