FYI, unfortunately, there is no standard method/process for factory resetting a Zigbee device nor a standard method/process for putting a Zigbee device into pairing/joining mode. Many manufacturers have their own unique way, and not all devices have buttons (some for example require you to power them off and on a specific number of times in a precise and timed manor, and some others will simply always go into pairing/joining mode for a few seconds every time you manually power-cycle them as in removing the battery), and many manufacturers even differ in their methods/processes from model to model of devices. You really need to read and follow the manufacturer instructions for every device or try to find someone online that have posted how to do it for that specific device model (you can seach on the device name and model here, on Discord, or Reddit).
I also have a copy of that video here too → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage
My advice for getting started with the best experince is to buy a few dedicated Zigbee Router devices like the IKEA Trådfri Signal Repeater to act as the (stable) backbone of your Zigbee network mesh.