You can add extras to an entry you have already bought without contacting anyone.
Sign in to your Race Space account, using the same email address you bought the entry with. If you are not signed in, select REGISTER/LOGIN from the main menu. If you are already signed in, your email address is shown at the top of the main menu.
Select MY ENTRIES from the main menu.
Find your entry and select Entry Actions.
Select ADD EXTRAS, the last option on the menu.
Choose what you want and check out.
If your entry is not registered yet
You do not need any of the above. Complete your registration in the normal way and add the extras as part of that process.
What is available varies by event, since each organiser chooses what to offer. Extras might include merchandise, camping or transport.