English Standard Version
“‘And I will give you shepherds after my own heart, who will feed you with knowledge and understanding.
I will give
Conjunctive waw | Verb - Qal - Conjunctive perfect - first person common singular
Strong's Hebrew 5414: To give, put, set
Technically, נָֽתַתִּ֥י is not past tense. It is in Qal perfect tense/aspect. It is most often translated as past tense in English. There is an exception as it is in this case.
Because Jeremiah is pronouncing a prophecy here, it is considered as the prophetic perfect tense where a Hebrew perfect can be translated into English future tense. See https://en.wikipedia.org/wiki/Prophetic_perfect_tense.
With one except, all versions in https://biblehub.com/jeremiah/3-15.htm translate it as future tense.
Young's Literal Translation
And I have given to you shepherds According to Mine own heart, And they have fed you with knowledge and understanding.
Who are the “Shepherds Like-My Heart”?
In the past, before Jeremiah was born, God had given them David who was after God's own heart (1 Samuel 13:14) to shepherd Israel. In the future, God will give more shepherds after his heart. The great shepherd was Jesus.
"I am the good shepherd. The good shepherd lays down his life for the sheep.
Further, Christ promised us the gifts of sheperds/pastors to the church.
So Christ himself gave the apostles, the prophets, the evangelists, the pastors and teachers,
Some of these pastors will lead us with knowledge and understanding as prophesied by Jeremiah.