New South Wales
The important thing is that you keep the other non-Agenda Side Mission that you didn't choose as active. You reshuffle and draw a new card only to replace the one you completed. Here's the rules relating to all the above:
RRG - Mission Stage - Post Mission Clean-up wrote:
- Return the Mission card corresponding to the mission that
was just resolved to the game box.
- If players just resolved the introductory mission, shuffle the
Side Mission deck. Then draw two cards and place them faceup
on the table. These are now active missions.
If players just resolved a non-agenda Side Mission, shuffle
the Side Mission deck, draw one card, and place it faceup on
the table. This card is now an active mission.