'Spelled' if you are from the US. 'Spelt' in most other English speaking countries
Happened
The past tense of "have" is "had."
The word "happened" is the past tense form of the verb "to happen".
have in past tense is had
The past tense of have is had.
Happened is the past tense of happen.
The past tense of 'spell' is 'spelled'. 'Spelt' is also used in British English.
You spell the past tense of settle like this: Settled
The past tense of happened is happen.
The past tense of happen is happened.
The past tense is coasted.
The past tense is paddled.
The past tense is traveled.