Nginx reverse proxy - pretending a different URL

Hy all

I'm a beginner in nginx reverse proxy things, so excuse the maybe dump questions.

We use a nginx as reverse proxy to access several web applications form unsecure zones.
I type in jira.example.com and it goes through firewall, reverse proxy to the web application. But for internal use we use the different URl jira.example.int (which is defined as baseurl inside the application).
Now atlassian jira takes intensive usage of the baseurl configured, the app will not work as needed if the URL is wrong / does not match the baseurl.

Question: how can I "pretend" the URl jira.example.int although I use jira.example.com?
I thought it'll require something like url rewriting but I'm really not that good in this proxy thing. And our specialist isn't around right now.

thanks in advance for any help or suggestions