Restart a Mission or Assignment in any Mass Effect games

(You're on the wrong part of the website, here is the Mass Effect 1 help section.)

There're two solutions to restart a mission.

Automatic save from the latest mission you started/completed, or sadly, load an old save if these missions you're talking about aren't the latest you've done.

But for missions on a visitable place (like the citadel), as long as you don't have completed it, the task will still be active.

For the mission "Crime in Progress", after you meet for the first time the Quarian/Volus/Officier, you have to talk with the seller where the volus has lost his datapad.

After you've talk to the seller, he gives you the datapad and then you can go back to the officier.

If you've already done that, you should probably load an old save as there's indeed a bug, before you've started these missions.