REGISTER or login:
Reset your password on what? An application, your PC?
Please give us a little more information.
In general, you can only reset your tablet back to its factory settings. You do that by following whatever the instructions are for your particular kind of Android tablet. Your owner's manual should have instructions. If not, then you should find a community forum or Support forum for the manufacturer of your tablet.
It might be possible to get control of your tablet back without a reset, but it depends on how you registered your device or what you installed to help with recovery. We have no way to know what your device setup is.
And sorry about asking about "REST APIs", but the REST APIs are meaningful APIs that just don't normally have much to do with passwords on a device (though it could be possible).