Open the Settings app
Tap About phone
Check the Model name or Model number
Look at the back of the phone or SIM tray for the model number
Check the original box or purchase receipt
Dial *#06# to view the IMEI, then match it with the model details in Settings
Use the Oppo support app or official Oppo website with the IMEI or serial number
Check the sticker under the battery if your Oppo phone has a removable battery