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Hi! My name is XXXXX XXXXX I can try to assist you...but be advised to do everything very carefully, slowly and precisely or you could make a mess! In order to reset the sync, you have to fully relieve all pressure to the mechanism. The safest way is to simply rock the pendulum manually until all tension is gone...but that can take hours, depending on the type of clock you have and the size of the spring. If the spring is within a casing, you can sometimes remove the works from the clock body and release the spring tension directly...but this is not a move for amateurs if the casing does not fully contain the spring...it can "jump out" at you and is a bear to pack back in....
You DO NOT want to reapply tension with the key or try to reverse it that way because you could easily strip a guide .... my suggest is to make sure the clock is level and bump the pendulum manually until it is totally released (and hope the spring did not slip or break from the overwinding or lose memory)....once it is unwound, only wide it about 50% until you are sure the tension is still good.
Hope this helps! Best, Will