The AUMID is an ID which is assigned for each appliication installed on a device. It is used e.g. in the Kiosk multi app mode to select apps. Which possibilities exist to get this AUMID I want to explain you in this blog.
Possibility 1
Press WIN + R to open a Run dialog. Tipp in the following command and click OK:
shell:Appsfolder
A folder opens in which all applications are located

Press F10 and click View -> Choose details

- Select AppUserModelId and click OK

- Change the view to Details

Here we are. Here you can see the AUMID

Possibility 2
Open a Powershell and enter the following command:
get-StartApps

Possibility 3
Open the Registry Editor. Press WIN + R and type in regedit and click OK

Navigate to HKEY_CURRENT_USER\Software\Classes\ActivatableClasses\Package

Also here we can see all the AUMID.
Stay healthy, Cheers
Jannik