How do i reset the Audi A3 limp mode?

If Your AudiA3 is in limp mode, the only thing You can do to "reset" it is to fix the problem that put it there in the first place. Limp mode is a feature that protects Your transmission from serious damage caused by a failed or failing component; as such, You don't want to exit limp mode until the necessary repairs or replacements are made. If You're confident that the failed component is no longer an issue, You should simply be able to place the vehicle in park and turn it off for 1 minute or longer. When You restart the A3, if there are no transmission problems to be found, it will not re-enter limp mode; it will have effectively been reset.