Hello,

I am in the quest "The Order of the Virtuous Blood". I killed Roland as Seridur told me, but now I have decided that it would have been better that I kill Seridur instead.

Is there a way to reset this quest by a console command? (I do not have a previous save game). I want to become an honorary member of Virtuous Blood!

No-- sorry. You can't use console commands to move backwards in a quest-- only forwards. Once it's done, it's done.

Unfortunately, all you can do is take the lesson that it's important to have multiple, regular saves, so that you always have something to which to revert later if you need or want to.

Sorry.

All you can do now is reload a previous save before you killed Roland.

The golden rule that applies to any game

Or you could continue on having learned the lesson not to trust Vampires. They can be very persuasive you know.
Or perhaps you wish to become a vampire yourself. Killing Roland will hardly matter in that case..