I am guessing here but since you have to hold the high beam switch to get them to work sounds more like the issue might be in there and not the switch.

 

I would double what Ralph said. Check the wiring going to the multi-function stalk and see if any of it is burnt out. If not its likely that the contacts in the switch have come to their end and you need a replacement. I would recommend (as would many others) that you purchase a headlight harness once you have this issue solved as it will help to prevent lighting issues going forward. The harness takes the input from the original wiring but using relays, removes the current load from the switches to prevent burning out or melting.

https://www.ebay.com/itm/CERAMIC-H4-...-/330997592807

 

Mine would work on high beam but not low turned out it was the plugs on the head lights. Soldered in some new ones everything is a ok.