When i was younger, i had a bad experience when i felt i was demon possessed. i still have bad memories and it causes me fear. how do i fix this?

Anxiety issue: Imaginative children can experience scary thoughts but continuing to suffer from the fear suggests anxiety issues have perpetuated the experience. Anticipatory fear that this may recur is also debilitating. Seeking professional advice in person helps stop the cycle and gives tools to an individual that are specific to the triggers and severity and frequency of the fear.

Counseling.: You should seek counseling for this. You need to speak this out with a professional. Seek a counselor or psychotherapist.