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If you are afraid that the engine will not rotate and the belt looks as if it will jump over, you should not start anymore.
Here the belt cover must be removed and the timing set. Then you have to see why the belt jumps over (cracked, tensioner defective, pulley defective).
Furthermore you have to check if the pistons did not hit the valves. If so, you have engine damage. Then the cylinder heads must be dismantled and the pistons checked. If the pistons are still ok, the corresponding valves must be replaced.
However, a mechanic should take a look at the whole thing on site,
I would be very happy about a rating with 5 stars over the star bar at the top of the page, without this rating the site operator does not pay us experts.