Could be just a simple adjustment to tightening the shift lever.
Does the lever move, or is it loose ?
Does 1st gear work ok if you are on a flat or slight uphill grade ?
Posts some pics.
You need either 10 posts or you can put the pics in your " gallery".
I do not know how to do this myself.
Most people on the great forum do, and will" chime in " soon to help.