It really depends on the length of your flashback (e.g. a paragraph vs a few pages) and the tense used in the rest of your story. However, it's common for the past tense to be used.
It's known as a tense shift. It could happen if a flashback is being used.
"is' is present tense. For past tense use was or were.
'Who' is a pronoun, it doesn't have a past tense. But you can use the word "was" as in "who was on the phone?".
I used the past tense to answer this question.
The perfect tense.
Flashback
Yes, typically a flashback is written in the past tense to differentiate it from the present timeline of the story. This helps the reader distinguish between events happening in the past versus the current events.
"The man had a flashback of his past after watching the movie"
It's known as a tense shift. It could happen if a flashback is being used.
Good writers don't usually use flashback at all, to be honest.
You use the past tense form which is 'had'.
You have to you have in present tense. You had to use had to write that sentence- use had in past tense.
I think flashback
Flashback
"is' is present tense. For past tense use was or were.
The past tense of "be" is "was/were." The present tense of "be" is "am/is/are."
Past indefinite tense