Electric adjustable seat

Hi I have a question about the electric adjustable seat in a MB 300 1993 (I think, it's my mother-in-laws). The seat is stuck in it's very back position. When I try to move it forward
nothing happens. When I move it backwards it just "jerks" a little. Please help. I need at least figure out how to release the seat so it can be moved forward manually. Thankful for all the help I can get.
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