I am not familiar with a PIR-101 model.
Are you referring to the 2GIG PIR1-345?
If the model label specifically says the model number is PIR-101, that might not be compatible. Can you provide a photo of the sensor’s label in reply here?
If it is a 345Mhz sensor that is not encrypted, you should be able to follow the general steps to pair a PIR1-345.
Those steps are here:
Are you getting stuck on auto-learn? Try tampering the device by opening the back plate when the panel is listening for a sensor.