just purchased used jd 5085m tractor and do not have a operators manuel.

[pwillis]

using a 7 ft rotary mower. set desired height but unable to set draft control.

 

[CobyRupert]

Not sure how or why you'd use draft control with a rotary mower, but if you do find out what draft control is, this is how to operate it according to manuals for your tractor that can be found online if you type "5085m manual":
Mechanical Draft Control:
With lever (B) fully FORWARD = No draft sensing. With lever (B) fully REARWARD = Reduces the amount of draft load required to override the depth setting (position preset by lever (A)).

 

[Tx Jim]

Draft control was designed to be used when plowing with a 3 pt implement but should not be used when height control of implement is desired such as mowing or blading.