What to do if my iPhone don’t want to install the update

It is likely that your iPhone is already at the highest iOS it’s eligible for. It can only update to 12.5.7. You can select Settings > General > Software Update. That screen will show you the current iOS. If the phone is eligible for an update, you will be prompted to do so. If you are not prompted, then your phone cannot be updated any higher. To get a higher iOS, you will need a new iPhone.