I will repeat what others have said - so maybe the moderator will actually try the solutions they are providing before wasting everyone's time with solutions that DON'T WORK.
These various links either go to QBO hype pages or download executable files that won't open.
I have moved to a different laptop from the original download of the app for windows desktop, when i converted from quickbooks desktop but they only give you ONE SHOT at installing the app... yet, the magic of the online version is to be able to use QBk on any machine.  Come on guys - LISTEN TO US.  When i follow the latest link sent i was able to download something that spins my wheels and gives me a message about being unable to connect.
Oh wait - that right - i can ask for help and wait for a call back for someone that doesn't know the answer to this SIMPLE QUESTION - where is the GOOD Link to add the app to ANY MACHINE i use QBO with?