For the Nether, you apply for Survivor, which is the first of the three Nether ranks. For the End, you apply for Voyager, the first of two End ranks. However, End rank applications are not currently being accepted because it has not been added to ECC yet.
Sounds good. Is the Survivor rank be less than a mayor, If so would I stay a mayor and the Survivor rank just be added on?
Yes. Survivor/Voyager/etc does not display in any case. The only difference will be your username color while in the Nether/End.