I agree with @bjoern__koth, it's much easier to implement GA in Launch, than AA in GTM. Launch has an easy to use GA/GTAGS extension, whereas GTM does not have anything for AA.
Personally, Adobe Launch is also much easier to work with and provides a lot more options...
However, that said, if you really want to implement AA using GTM, you will basically have to go back to the "old" way of implementing the tags.. this means adding the JS files into your page (AppMeasurement, or WebSDK files, etc), then you will have to set your dimensions and events manually, then trigger the beacon manually. Basically you will have to implement it as a stand-alone instance.
This documentation might also help:
https://experienceleague.adobe.com/en/docs/analytics/implementation/js/overview
I've been around long enough to remember how to do standalone implementations (at least using AppMeasurement (if you are trying to do WebSDK that would be an all new experience...), so if you have any specific questions I should be able to help you out.
Good Luck