nands_krish“As far as I know in both tenses are used when an action begins in the past but continues into the present / holds relevance in the present. ”
No.
Present perfect only is "used when an action begins in the past but continues into the present / holds relevance in the present".
Past perfect is used when an action began in the past but continued to another point in the past / held relevance at that point in the past.
Past perfect is the backshift of the past. It is also the backshift of the present perfect.
John said, "I saw that movie last week".
John said that he had seen that movie last week.
John said, "I've seen that movie several times".
John said that he had seen that movie several times.
CJ