First, you need to have navigated to the page on which you wish to have it disabled. Then:
1. Hit ALT to throw focus to the Chrome Menu button, then left arrow over until you find the uBlock Origin menu button (and, if you happen to have installed uBlock Origin Extra under Chrome, make sure that you're not on that button). Hit Enter to activate the uBlock Origin Menu.
2. Tab once to land on the "Disable uBlock Origin On This Page Button." Hit Enter or Spacebar to activate it.
3. uBlock Origin is now deactivated for that page until or unless you repeat this process again. The Disable button is really a toggle - if uBlock Origin is enabled it disables it and vice versa.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
A great deal of intelligence can be invested in ignorance when the need for illusion is deep.
~ Saul Bellow, To Jerusalem and Back