PLEASE NOTE THIS IS FOR THE 3 BUTTON UK CHIMES ONLY.
To pair an additional chime or to hold a new melody all you have to do is re - PAIR the receiver(Chime) and transmitter. If you choose a different melody or volume, then re-PAIRING will hold the new melody/volume. This is a feature of our chimes which allows people with more doorbells to program different Melodies for different doors using just one chime.
To re- PAIR please do the following.  
1. Choose the volume and melody you want. 
2. Now press and hold the mode button(the third button with recycle ♻️ symbol on it).  Keep holding it.  You’ll hear two beeps. You are in pairing mode. Keep pressing the mode button. While continuing to press the mode button, ring your doorbell, or momentarily touch the two wires that go to doorbell terminals. You may need 2 people or an extension cord so that you are close to the doorbell. You will hear one beep from the chime which means you are paired. Release the mode button. Test the chime by ringing the doorbell or by touching the wires again. It should ring now at the set volume and set melody 🎵.  Else repeat this pairing step.
3. Your chime will now retain this melody and volume for that particular Doorbell.