Recruit another person.
Remove the entire halyard.
Stretch out line completely roughly 75+ feet.
Hold one end tell your friend to hold the other.
Tug on it, give it a pretty good tug.
You will feel the twist in the line in your hands.
Work the line, untwist it little by little.

OOOORRRRR go the extreme route.
Remove the entire core where the line runs through the blocks. Leave the core and remove the jacket where the line runs through the spinnaker. The twist in the line will be minimized to nill.