Question

Ayer tú (cantar) una canción. vas a cantar cantaste cantaré cantabas

Answer 1

Ayer tú (cantar) una canción.

Yesterday you (to sing) a song.

Answer: Ayer tú cantaste una canción.

Yesterday you sang a song.

Cantaste is 2nd person singular which matches tú (you).

Answer 2

“Ayer tu cantaste una canción”
Means: “Yesterday you sang a song.”
So cantaste is the best answer for you to choose in regards to this sentence.