1°- Subscribe the mission

2°- Open Arma 3 downloded missions files directory on your pc
\Documents\Arma 3\missions

Tutorial for find the directory -> https://www.youtube.com/watch?v=Gr1vNjkJmyM

3°- Take "OPTRE: Corvette interior" mission file.

4°- Import the file on your save mission directory
\Documents\Arma 3\UserSaved\missions

5°- Download & install PBO Manager
http://www.armaholic.com/page.php?id=16369

6°- Open the file pbo "OPTRE: Corvette interior" with PBO Manager.

7°- Take mission.sqm file and copy this in the OPTRE: Corvette interior Folder

8°- Play arma 3

9°- Open 3d eden editor

10°- Load mission OPTRE: Corvette interior

11°- Select and Save the Custom Composition !

Tutorial video for create a Composition -> https://www.youtube.com/watch?v=HjKURvNhfJ4