Here is what the GS-911 support says about how to manually wake up the sensors:
“Option 3: waking a sensor manually (does not always work!)
As the sensors are still active for a while before going to sleep, your first thought would be to take the bike for a short ride, thus waking the sensors and allowing you to learn a sensor.. This however is NOT THE RIGHT WAY!! This will wake both sensors and when you instruct your RDC unit to learn a specific position, e.g. front wheel, Set A, the control unit will be receiving signals from both active TPM sensors and might not learn the right one, or any for that matter...
THE CORRECT ALTERNATIVE, also known as the "ALERT method" is to let the air out of the wheel rapidly (we simply depress the valve for around 10 seconds)... this rapid fall in pressure wakes the sensor and places it in an Alert mode, where it starts sending its data (which obviously includes its Sensor ID!).
Thus, to summarize, if you do not have a RDC wake-up tool, either enter the new Sensor ID manually in the Advance section (this of course assumes you noted the Sensor ID before refitting the wheel ;-) ), or when the GS-911 application asks you to use the wake-up tool, simply depress the valve of the tire that you want to wake for around 10 seconds, which will in turn wake the sensor in an Alert mode where it then sends its Sensor ID and pressure information....”
I guess - in doing that wake procedure, you will never get the actual pressure in the tire or know when you have it set where you want it - unless you do a massive overshoot on inflation first. I do carry a gage with me. Easy day.