How to access a method of another app in my controller?

I want to acces a method of another app in the controller in my app.
I’ve tried it with the link to method, but it doesn’t work.

Can anyone help me with this issue?
Or is it even possible to access another method?

It might be technically possible but it’s making one app depend on another and therefore an anti pattern.

How are the apps related? Is there a way to do your process through some public API abstraction or a HTTP request?

I have an administration settings app, where i fill in Data to a Nextcloud-User like the company or the username in a ticket system. These informations are saved in a database.
I have another app, where the user can enter an issue via Nextcloud and in the Controller I want to use the database of my first app to automatically fill in the username of the ticket system. I wanted to achieve this via calling the show() method to search in the DB.

I hope you understand what I mean. Unfortunately I can’t publish my code anywhere.

Does anyone know if this is possible or can help me please?

Please keep in mind that due to Nextcloud’s license your app will have to be licensed MIT, AGPLv3 or a similar compatible license.