Create 2 metasound soruces files, name as part 1 and 2, together with music files 1 and 2
In metasound part 1, set as below
In Part 2:
To let part 1 music loop once trigger on, set as
To part 2, set to let the part 1 off once enter part 2
Back to part 1, add below
Now when part 1 turns off after go to part 2, part 1 play once more, then go to part 2
to part 2 after part 1 turn off, now tick it as loop
Create 2 trigger boxes in the scene
In level BP, set below
Note it must trigger box 1 first and then to box 2. No response if directly trigger box 2