I am struggling to make sense of your post, but let's see if I understand you correctly:
a) It's only the screen that's affected, right?
b) Is the HP a 2-in-1 or a traditional clam-shell?
c) Does the HP work now, or is it completely dead?
d) You can hear sound but there's no video signal, right?
My guess is that coffee has trickled down behind the bezel (the plastic frame) and messed with the video or flex cable.
Best case scenario: Remove the power cable and the battery (if possible). Then remove the bezel and unclip the flex cable. Use soft tissue material, like Kleenex (NOT a towel!) and dab the flex cable as well as the area around the flex cable mount. Leave the computer to dry. After an hour or so, re-assemble the computer and see if the screen works.
Not-so-good scenario: The flex cable is defective and needs to be replaced. You can get these cables on Amazon and eBay.
Worst-case scenario: The coffee has seeped all the way down to the system board and shorted the flex cable mount. And that's probably the end of the road for your HP. If the HP is still under warranty you might be able to have HP's tech support install a completely new system board.