The permission WRITE_SECURE_SETTINGS is required to use this app. To grant it run this command:

adb shell pm grant com.draco.smresolutionchanger android.permission.WRITE_SECURE_SETTINGS

WARNING:
I will not be held responsible if you crash your device by using an unsupported resolution or density.

I recommend taking a screenshot in case you need to enter your default settings and the default button isn't perfect.