You need to go through the following procedure:

1. First download the forms from the DCC website
2. Read through the information
3. Find 3 people willing/able to shutdown the station within 30 minutes on request from Ofcom
4. Fill in pages 10,11,12 (at time of writing)
5. Post the forms to RSGB as stated in the downloaded document.
6. Once the NOV has been issued for the MB7Uxx callsign you need to inform RSGB that you intend to switch on your station in 14 days time