"Have" is an irregular verb in English. This means that its past tense form ("had") and past participle form ("had") do not follow the typical pattern of verb conjugation.

hear, it doesn't change because it is already in present tense. However, if you were talking in past tense, it would become heard.

Yes, "smiled" is an irregular verb. The base form is "smile," and the past tense form changes to "smiled" rather than adding "-ed" as with regular verbs.

It depends on what you're writing. If you're writing a novel then it's a common technique for writer's to change tense. For example, if you are primarily writing in present tense, you could switch to past tense when talking about something that happened previously.

If you are writing something academic (such as an essay or thesis) then you should try to remain consistent with your tense and not switch.

Changing your tenses too often will confuse your reader so be careful.

"had felt" is in the past perfect tense. It is used to show an action that occurred before another action in the past.

The present tense of "will be doing" is "am/is/are doing." For example, "I am doing," "She is doing," "They are doing."

The past tense of "bite" is "bit." The past tense of "put" is "put."

The first person present tense of the word "lock" is "lock."

The past tense of "attend" is "attended," and the present tense is "attend." For example, "She attended the meeting yesterday" (past) and "She attends the conference every year" (present).

The past perfect tense of "assist" is "had assisted." It is formed by combining the auxiliary verb "had" with the past participle form of "assist."

The present tense of "swear" is "swears."

The past perfect tense of "flee" is "had fled."

The present perfect tense of "listen" is "have listened" or "has listened."

The present perfect tense of "mark" is "have marked" (for I, you, we, they) or "has marked" (for he, she, it).

The past tense of the word "cross" is "crossed."

The past tense of "swing" is "swung."

The past tense of the word "speak" is "spoke".

The past progressive tense of "ring" is "was ringing" or "were ringing," depending on the subject. For example: "I was ringing the doorbell" or "They were ringing the bells."

Scare is present tense. The past tense is scared, and the future tense is will scare.