You can do it multiple ways, you can go to the Stremio add ons page and find what you want, click on it and then install and configure, then copy the URL and paste it in the add ons of the STRMR site.
You can go through and set up the AIO set up with what you want to add in, nice things is you can add different add on into it and only need to copy and paste your debrid API one time.
I use this. When you get to the quick start choose Manifest at the top instead of Stremio, that will give you the URL you will need to paste in the add ons section on the site.