You don’t choose a a lounge, lounge key isn’t per lounge. In the app if you enter the airport you’re at or going to, it’ll show you what lounges are there and allow you to click them for more info, but you can skip this at the top right:
You then generate a QR code which is a standard lounge key pass. So yes if there’s 3 lounges available in the airport you can go to any of them - you can’t enter one, leave it and go to another on the same pass. The only requirement is you use it on the day of your travel and have ID - you specify the name for each pass.