Z offset calibration with TFT35 E3 - how?

Hello,
Just a inquiry for some information about the Z offset calibration with the TFT35-E3 "touch mode".
Is there somewhere a tutorial (or video) available for this process. I couldn't find any. :-(

I know a video for the marlin mode (but that mode is currently not working on my display).

Any suggestion is much appreciated.
TIA