Need to have the Sub Menu that opens ability to scroll when lots of Sub menus

HI

I have a client that has MENU like this:

BRANDS Drop Down Accordian

In here we have over 30 Brands on each line.

When we OPEN the BRANDS section and click on 1 Brand, then the Menu CLOSES .. We don’t want that, that is a pain. It needs to stay OPEN, and then we ALSO need the option to SCROLL down with a scroll bar on the right side, as we have over 30 Brands, the Accordian opens up too far down the screen like a snake, therefore we would PREFER to have the Sub Menu shown at certain height, and then an AUTO scrollbar can be seen on the right to continue down.

I have this set up in another section of client site BUT it is NOT working in the Wholesale area and I cannot remember HOW we set this up with your plugin years ago.

Then I have other Categories underneath.
CANDLES
ELECTRICAL
FURNITURE
etc

I have Customer side for login and Wholesale side for Login.
It works NO issues on Customer side non wholesale.
But for the life of me, cannot remember HOW I did it last time.

If someone could help that would be great.

Thanks
Kristin