Oil & Fuel 90c case 2015

[sirchancelor]

I have a case farmall 90c tractor that has reduced power with the stop code flashing and going steady. Have DEF/AdBlue quality concentration display and a def/adblue tank has been empty symbol (that could be multiple things). First the tank has not been empty. It says to drain the tank. How should this be done? Does it have a drain plug or do in need to take the tank off, or with syphon hose. Any help would be greatly appreciated.