Do you have your low bar kip? I know my dd struggled with the high-bar kip, too and found that if you really swing out after catching the high bar, the momentum helped her get that kip. Just keep practicing, it will come! Good Luck!!
It's kinda hard to help you without any details on where you're at.
Also, I've actually experienced the opposite -> try to swing with less momentum... kind of drop down into your swing, instead of swinging as you would in a tap. But that pretty much depends on height as well. If you'Re short and have to really jump to catch the high bar you're forced to do a pretty big swing or it'll feel weird.
I agree with grizzoline. Often the reason why the high bar kip isn't working is because there is too powerful a tap swing in front of it. It needs a different type of swing to the long hang pullover or giant.
When you jump to high bar try to keep your feet behind you for longer and dont do a hard tap swing. I have found that many kids have gotten it straight away when they try this.