Install the [TH] Q&A Forums add-on as specified in the documentation.
Next, you'll want to ensure you've set the Q&A status on the necessary forums as votes for posts in other forums will NOT be imported.
Navigate to Tools → Import data in your XenForo 2 Admin CP.
Select the "[n] Best Answer / Q&A System" importer.
After confirming everything was imported correctly, go into Tools → Rebuild caches and run the "Uninstall [n] Best Answer / Q&A System add-on" tool at the very top of the page. This will remove any data created by this add-on, as well as removing it from the add-on list.
If you need assistance getting the add-on installed and imported or would prefer us to handle it for you, you can create a ticket.