Based on the information you provided, it seems like you have a fake iPhone with an iOS skin but running on Android, and you want to install a stock ROM on it. Here are some steps you can consider:
1. Identify the Model: Since you mentioned it has Android 5 and a Mediatek chipset, you can try to find the specific model of your device by checking the settings or the back panel for any model numbers or names.
2. Download Stock ROM: Look for the official stock ROM for your specific device model from trustworthy sources like the manufacturer's website or dedicated forums for custom ROMs.
3. Enable USB Debugging: If you are unable to enable USB debugging through the settings due to the iPhone-like interface, you might need to find an alternative way to enable it. Sometimes, dialing a specific code in the phone app can enable USB debugging.
4. Flashing the Stock ROM: You will need to use software like SP Flash Tool or MTK Flash Tool to flash the stock ROM onto your device. Make sure to follow a guide specific to your device model to avoid any issues.
5. Backup Data: Before flashing the stock ROM, ensure to backup all important data on your device as the process might erase everything on it.
6. Brick Risk: Flashing custom ROMs or stock ROMs involves risks, and there is a chance that you might brick your device if not done correctly. Proceed with caution and make sure to follow the instructions carefully.
It's essential to note that modifying your device in this manner may void any warranty it has left, and there is a risk of damaging the device permanently. If you are not confident in following these steps, it might be best to seek help from a professional or a service center familiar with handling such devices.
PH