Follow these steps to erase all the information from your iPhone. If you erased your cellular plans during this process and you want to reactivate your plan on the Dual SIM iPhone, you will require a new eSIM card.
Go to Settings > General > Reset.
If asked, enter your passcode or Apple ID password.
Confirm whether you want to erase everything or erase everything but keep the eSIM plans.
Wait for the device to erase. Depending on your device, it can take a few minutes to erase your data.