If you submitted it out of the game, the number should be in the subject in brackets when they reply to it. If it's not, you could try just sending a second ticket to add information. I don't know if replying directly would work but I don't think the address includes "no-reply" like most companies.

If you submitted it in the game, there is a history tab to track it and the replies and you add information either by replying to it or submitted another one. What they will do is just append the information to it.