Launch X431 IMMO Plus/IMMO Elite/Immo Pro supports Volvo XC40 2018-2021 add key and all keys lost. Here is the guide to add a spare smart key to XC40.
Select Volvo->XC40->2018-2021->Smart Key
Check Operation guide
IMMO plus will show you operation guide and wiring diagram
To add key, need to remove CEM module
Connect x-prog3 with CEM module follow the wiring diagram
Save data
Select Smart Key Add function
Turn the START knob to the right one time and then release it.
Place a smart key to be programmed in the cup holder, take other keys out of vehicle
Add key successfully