Sure, it would be unusual for a random individual controller to be able to give instruction on landing a 747.
But I can guarantee you that they would arrange for someone who did to help you. For immediate help, there would likely be another pilot in the sector that that controller could ask to help keep you in the air. While that is happening, other controllers or supervisors would be calling the airline to get a type-certified pilot/instructor on the radio to talk you through the landing.
I don't know of any cases where it has actually happened on a commercial, but there have definitely been cases in light aircraft where the pilot became incapacitated and ATC talked the non-pilot through a safe landing.
But I can guarantee you that they would arrange for someone who did to help you. For immediate help, there would likely be another pilot in the sector that that controller could ask to help keep you in the air. While that is happening, other controllers or supervisors would be calling the airline to get a type-certified pilot/instructor on the radio to talk you through the landing.
I don't know of any cases where it has actually happened on a commercial, but there have definitely been cases in light aircraft where the pilot became incapacitated and ATC talked the non-pilot through a safe landing.