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noglider has it right credit and build
small steps, don't worry about off road, hills and hard stuff. that was where you were before and where you are working too.... go out and ride on the street or paved trail.... keep it short, with low gearing so is it is easy to pedal, don't worry about speed or distance.
go out small distance and come back (or around the block one), next day go a little farther.....keep it up so there is no re-injury, just enjoy the short ride and build up