Hi Jan & welcome
You'll be out of luck with your TF101G, I don't believe there was much if any custom development for this 3G & wifi model. Any custom rom you install for the wifi only model will mean you loose the 3G cellular functionality.
Your best bet is to backup any files you may have & then follow the Factory Reset guide linked in the Master Help Guide. If you follow the guide fully, you will end up with a device that works as well as it can. Sadly though, given this is a 2011 model, it is now going to be badly out of date & will appear relatively slow and unresponsive when compared to modern devices. 5 years is a lifetime or more in tech terms.