Where in scripture does it say that the throne of David is in heaven????
29 "Men and brethren, let me speak freely to you of the patriarch David, that he is both dead and buried, and his tomb is with us to this day. 30 Therefore, being a prophet, and knowing that God had sworn with an oath to him that of the fruit of his body, according to the flesh, He would raise up the Christ to sit on his throne, 31 he, foreseeing this, spoke concerning the resurrection of the Christ, that His soul was not left in Hades, nor did His flesh see corruption. 32 This Jesus God has raised up, of which we are all witnesses. 33 Therefore being exalted to the right hand of God, and having received from the Father the promise of the Holy Spirit, He poured out this which you now see and hear. 34 For David did not ascend into the heavens, but he says himself: 'The Lord said to my Lord, "Sit at My right hand, 35 Till I make Your enemies Your footstool." ' 36 "Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ." (Acts 2)Peter says that Christ was raised up to be seated on David’s throne. Peter argues that we know David is dead, and Christ is the fulfillment of the David’s promise, then Christ must be seated on David’s throne now. The evidence is the outpouring of the Holy Spirit on Pentecost. Again, Peter argues that if Christ’s is not reigning then by what authority is the Holy Spirit given?
The "throne of David" is a symbol used to represent God’s legitimate rule over His people (cf. 2 Sam. 3:10). Christ’s rule has certainly begun over the house of Israel in that many thousands from Israel in that day and moving forward have come to acknowledge Christ as King. If Christ is not seated on David’s throne then Peter was certainly misinformed.
The NT writers certainly understood all these things (throne of David, tabernacle of David) as signs and symbols of Christ’s present reign over not only Israel but all the nations.
6 For unto us a Child is born, Unto us a Son is given; And the government will be upon His shoulder. And His name will be called Wonderful, Counselor, Mighty God, Everlasting Father, Prince of Peace. 7 Of the increase of His government and peace There will be no end, Upon the throne of David and over His kingdom, To order it and establish it with judgment and justice From that time forward, even forever. The zeal of the Lord of hosts will perform this. (Isaiah 9)31 And behold, you will conceive in your womb and bring forth a Son, and shall call His name Jesus. 32 He will be great, and will be called the Son of the Highest; and the Lord God will give Him the throne of His father David. 33 And He will reign over the house of Jacob forever, and of His kingdom there will be no end." (Luke 2)