When leveling up my character I roled a dice to determine what I would add. It was higher then the average. I updated it on the character sheet to be the proper health from my role. Every time I use the long rest feature to reset everything it changes my health to what the average is. How can I permanently change my health on my character and not have it reset to the average on every long rest?

In the character editor go to the "Home" section and scroll down to "Hit Point Type" and make sure it's "Manual". Fixed will set it to average every level (except first which will always be max)

Then once you've done that - go to the "Class" section in the editor and click "Manage HP". In the "Rolled HP" box put the combined total value of the dice you have rolled for your levels. Remember that first level will always be max. Do not include your Constitution modifier as it adds that automatically after.

If there's anything in the Override HP value - remove it. That's for effects that reduce or increase your maximum during normal play - not for setting your HP permanently.

Also when long resting, you could have unchecked "reset maximum HP during this rest" to prevent the max HP from resetting during the rest (...pretty self explanatory really).

Though the way it is meant to be done is how Emmber explained it.