They can drop a prosecution at any time, and you can write to them any time, but they may not do anything until the court tells them the conviction is void.
It may help people on here if you say what you were convicted of.
I'm not quite sure what you mean has happened about the declaration. Maybe you mean the staff are setting an appointment for you to make the declaration before magistrates in court, or before a court officer.
So i have been charged with being in a compulsory ticket area without a valid ticket. Under byelaw 17 (1) of the TFL railway byelaw made under paragraph 26 of schedule 11 to the Greater London authority act 1999, and confirmed under section 67 of the transport act 1962.
The declaration has been sent to the magistrates court and they will give me a court date to come in and sign an oath saying I had no prior knowledge of the charge, penalty fare etc. I will then be asked to enter a plea of guilty or not guilty. I'll be seeking legal advice this evening (the solicitor has a drop in centre for free advice) and will see what they say about writing to TFL etc.
The woman I spoke to on the phone at Single Justice said there's absolutely no way it can be settled directly with TFL out of court, I am really hoping this isn't true.
If I plead not guilty I'll have to fight my case (with no solid evidence, only what I've previously mentioned), and if I plead guilty the fine is reduced by 33% and no agro of fighting my case, however I'm very worried that I will have a criminal record