This is what you do ....
I have a pup who wants to jump the gun ... so to speak too
Either sitting or standing say Sit ......
what helps is your hand movement
hold the treat toward them first and then curl your hand upward
this helps them to sit and not jump so much
But ... if he jumps
It's No .... and pull the treat away until he gets down and calms down
repeat it again and again
Do Not give him the treat without the sitting