Re: need info about my 1990 90hp
Some controls, you press the disc with the "OMC" on it inward while moving the shift lever forward. Others have a similar function button located on the binnacle housing elsewhere. Some have no button, but the entire lever is pulled outward, then forward to advance the throttle. I've yet to see one without this feature, although it's been implemented in different (and sometimes non-obvious) ways. Is there a large button on the binnacle housing just inboard of the throttle lever? Can't tell from your picture.
A quick stop at any BRP dealer should demystify the situation in a hurry.