As i understood this: https://muidev.de/wiki/TracTickets
you need some extra permissions.
However, some Trac installations may put restrictions in place about who can change what. For example, the default installation doesn't permit to non-authenticated users ("anonymous" users) to change anything, even to comment on an issue, for obvious spam prevention reasons. Check the local contributing policy, which you can usually find on the front page WikiStart, or contact your local Trac administrator.