How do I change my ringtone on Samsung s8+

This would be because the files you want to use are not on the phone. You can't really access that when in the phone's settings to change sounds. You would actually have to access OneDrive outside settings and download the audio file you want to use to the phone. Then, after it has downloaded, you can add it as a ringtone. You cannot set up a ringtone, or other system sound, to use a file that is not on the phone.