Hi! I am having the same problem:
https://forum.yeelight.com/t/topic/24199
Any of you guys found a solution?
Pairing remote control to Smart bathroom heater.
I came here trying to find the answer to this but couldnt.
Worked it out eventually so am posting here.
Reset the heater unit by pressing the big round button for 5 sec.
The lights will turn on.
Then on the remote control, press the top row right most button together with second row left most button. Hold for 3 sec and it will initiate pairing with the heater.
You can download the Xiaomi Home app and also sync the heater to your phone.
Hope this helps.