I Have finished 3 of those but i don't know how to earn my reward or find commander Selyn.
Could it be a bug or something???
All you have to is "Hail" her. If you requested the "Investigate" mission from her and have completed the 3 of 3 missions then press the "L" button and select the "In Progress" tab. There will be a green check mark if you've complted the mission. Highlight and click the "Hail" button. Then follow the instructions in the dialogue window.