If you’re using C++, there’s this function: https://docs.unrealengine.com/en-US/API/Runtime/Core/Containers/ByteToHex/index.html
In Blueprints, I think you’ll have to write your own.
Left digit will be byte / 16. Right digit will be byte % 16.
Then you’ll need a function to convert values higher than 9 to letters from A to F, for both digits.