Sorry to hear that your Sentry safe is not working because of the lost combination. You can contact a local locksmith but they may have to break the safe open and then it will not be able to be used without repair.
Your question is very common on our site. The trusted and recommended way to retrieve your lost combination is to contact Sentry directly as they will be able to retrieve your combination for you. The contact info as well as instructions for retrieving your safe combination can be found here in this link below: