Help on how to do this would be greatIf im right, there are two connectors on the rear screen normally (can someone confirm ), one will be an earth and one will be a 12v supply, make sure you have a good earth and also check you have 12v with a voltmeter or circuit tester, both can be bought from a good motor factors.
Also check each individual heating element strip on the rear screen and make sure none are broken.
Im new to bmw's aswell but these are the checks i would usally do, oh and also check the fuse!!!
Hope this helps, let me know if you need an explanation on how to check the earth and power(12v).