How do you set up the phone using one SIM on a dual SIM phone?

To set up a dual SIM phone using only one SIM, insert the SIM card into the primary SIM slot as specified in the phone's manual. Power on the device, and it should automatically detect the SIM card. Go to the settings menu, select "Network & internet" or "Connections," and ensure that the mobile data and network settings are configured for the active SIM. You can disable the second SIM slot if desired to avoid any confusion.