Hi @Saad
If you have SIM card only in slot2 IMEI for that slot will be used otherwise if you have SIM card in slot1 or in both slots or no SIM card at all then IMEI for slot 1 will be used.
We will need to get rid of IMEI however due to Google policy (more info: Collect will need to stop using IMEI as deviceID and making simSerial and subscriberID available) and we are going to replace it with newly generated "Install ID" which is displayed in the latest version at the bottom of Form Metadata screen.