First you will need to connect SimpleRigResetter to motherboard of each rig (2 Power pins and 2 LED pins).
Then you will need to install small Agent software in windows or script in linux and set up SimpleRigResetter serial number and port that this rig is connected to.
This windows/linux agent software will send every few seconds small keepallive packets to SimpleRigResetter telling "I am allive, please dont reset me"
When SimpleRigResetter will not receive few keep allive messages within specified time (default 300 seconds) - it will turn off and turn on your rig automatically.
In my SimpleMiningOS there are special menu for enabling SRR Agent for rigs so it is even more simple :)
Beside normal reset function, there is also Long Reset function which powers down rig for more time (like 5 minutes) and then it turns it back on

Bitcointalk thread