How can I make tempo transition (adaptiv) music in UE4

So basically I have 2 trigger boxes. When I go in to the box_1 we hear music_1, and when I go in to the box_2 I want the music from music_2 to play instead of music_1.
But I want the transition to be in tempo and not switch directly when I go in to the box. I want the music to finish their bar before they transition to the next music_x
Anyone know how to do this?

//M.Viklund