GM service manuals are definitely recommended with a Tech 2.
The definition of the Top Relearn mode has been posted previously, so it's easier for you to use the search function to find it than to re-write it. Here's how it's performed:
Top Relearn Procedure
Navigate to:
Vehicle Control Systems/Computer Integrating Systems/Module Replacement/Setup/FTC Module
1. Select the Folding Top Learn Procedure soft key
2. Move the top through one complete cycle to store the new sensor parameters.
3. Subtract at least $125 from the price of the tool and books each time you perform steps 1 & 2.
It's useful to maintain a log of the sensor values for later comparison to determine when one is on the ragged edge.
CCC