'Spelled' if you are from the US. 'Spelt' in most other English speaking countries
The past tense 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.
The past tense of 'spell' is 'spelled'. 'Spelt' is also used in British English.
Happened is the past tense of happen.
You spell the past tense of settle like this: Settled
The past tense of happen is happened.
The past tense of happened is happen.
The past tense is traveled.
The past tense is hoorayed.
The past tense is roped.