[otrs] automatically fill of TicketFreeText

hello otrs-gurus, I have following problem: I add TicketFreeText at Ticket. Now, I want that this TicketFreeText gets a value from my databyse automatically. This value is a unique value in database (number of contract). I tried to found some documetation but without success. *there is TicketFreeFieldDefault.pm in /opt/otrs/Kernel/System/Ticket/Event, wich has two subs (funktions) but that doesn´t help me, i can´t understand it. thanks for your answers!