The past perfect tense is had collected.
The past tense of collect is collected.
Existed is the past tense. The past perfect tense is had existed.
"Has collected" is the present perfect tense of "collect" used for third person singular subjects.
Present perfect is formed with --- have/has + past participle.Because collect is a regular verb the past participle is verb + -ed = collected.So present perfect is have collected or has collected egHe has collected his pay.They have collected the rubbish early today.
If you meant what is collect in past tense, It is collected.
The past tense is bled, and the past perfect tense is had bled.
The past tense of sit is sat; the past perfect tense is had sat.
The past perfect tense is "had confronted".
The past perfect tense is had chosen.
The past perfect tense is had burned.
The past perfect tense is had set.
The past perfect tense is had rung.