It’s easy to invoke the App Picker by pressing “Command+Tab”. This brings up a visual list of all your open apps. It’s easy to then tab through the apps to move to the app that you want to work with.
If the app you want is at the end of the list you can easily navigate the list backwards. Just pressing Command+` – that’s the back quote symbol moves you back through the list. If you’re struggling to find it, because keyboard configurations do differ, the back quote key also contains the “~” character.
Hint – it’s usually at the top left of the keyboard below the Function keys. On some laptops it’s between the Shift and Z keys on the lower left.