If I remember right so long as you own the bar all you have to do is buy them at Jessica's office under the bar's upgrade options same as everywhere else.
1 year ago (+1)
Did you already purchase the bar?
I just made my way back there from a fresh save and once I purchased the bar all the upgrades were made available for purchase. Sorry if this doesn't help but if you own the bar and still can't buy the upgrades then you should probably report it to Arc as a bug.