@DennisJung If you walk through a gateway install, it will get to a screen in which you can input a recovery key. This should pull in everything that existed on the gateway and automatically work... that is the whole concept behind a recovery key. When the gateway is installed, you should then have access to it in the Service...
No, not for me, i only have the possibility to install a new gateway.
Did you get any further with this - I seem to be having a similar issue. My server based gateway "company"_PRD disappeared, could not be recovered and was not visible on PowerBI Service, on 5th Nov. So I created a new one "company"_PROD,
Now last week, "company"_PROD has now disappeared from my server. However the symptoms are now that "company"_PROD is still visible on PowerBI.com against existing datasets, but not any new connection. Just to confuse the issue "company"_PRD has now returned for migration, but will not accept my recovery key.
Microsoft hinted that they are manually moving the gateways when upgrading the service, and after two calls they've pushed to the Dev team.
No, they couldn't help me, so i reconfigured everything and it works since back than.
Even the microsoft support didn't find any problem.
The strange thing about this problem is that the gateways still exisit, they appear sometimes in Flow / Powerapps.