I was playing a gig a few months ago when somebody knocked some of my equipment over, including my Motif rack.  The main L/mono jack got tweeked and now doesn’t work.  When I try to plug a chord into it now it’s not straight and very loose.  And, of course doesn’t work.  Either does the right main, even though nothing was connected during the fall.  So I thought I could just use the assignable output 1 instead, which works but isn’t the best solution.  I’m pretty handy with fixing things myself so maybe somebody can point me in the right direction.  Or, would it be possible to get the R output to work like the L/mono?

No. If there is any time that it is very clear your unit needs to go to the shop - it is now.

The R jack cannot be reprogrammed to be like the L/MONO jack.
The Assignable L/R cannot be substituted for the Main L/R

Get your unit fixed !!! Now is the time!