Just click the shifter as if you were going to put the chain into a smaller gear in back (provided it is not already shifted to one of the smallest gears). Two 'shifts' should be enough- don't pedal- you are not looking to actually shift, just to move the rear derailleur to a smaller gear. This should make some slack. Put the housing back into the stop, and shift back without cranking. Then check everything out (rear dropout not bent, no housing kinks...) and try shifting while turning the cranks to see how it works.
Tzvia- rollin' slow...
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