There is no past tense of past tense because it is not a verb. For instance, there is no past tense of the word 'desk' (there is no 'desked' or 'did desk', because desk is a noun, not a verb.
Or it could mean: Past perfect.
Past perfect is sometimes described as 'past in the past'. It is used to show that one thing in the past happened before another thing in the past.
Example: The race had finished before the rain started.
the past tense of am is was and the past tense of has is had
The past tense of "has" is "had" and the past tense of "have" is "had."
Was and were are both the past tense of be. The present tense is: I am he is you are they are The past tense is: I was he was you were they were
"will be" is the future tense of "be". The past tense of "be" is "was/were".
The past tense is she did.
The word "were" is past tense. It is the past tense of the verb "to be."
The past tense of "will" is "would". The past tense of "to be" is "was" or "were".
The past tense of "you will not" is "you would not."
The past tense is had.
The past tense of "am" is "was" and the past perfect tense of "has" is "had."
HAD is the Past Tense of TO HAVE.
Existed is the past tense. The past perfect tense is had existed.