Dear Majken,
It's good to see that you are proceeding well with your initial double/multiple coding exercise.
To answer your questions:
1. Since the 25 items are the only one currently "completed" for that code-set, you can: in the "review statistics" tab (lower right corner), expand the screening set inside the "Completed Coding" box and click the "no entry" red symbol on the row that corresponds to the person that owns the completed version. This will uncomplete the coding for the 25 items. Note that this works only because no other items have been completed, as it doesn't allow to choose what items should be un-completed in detail.
1.b for everyone's benefit, in all other cases, the procedure would be: on the collaborate tab, click on the "allocated" number for the appropriate coding assignment, open the first item on the list, right click the code-set that needs to be un-completed, choose "Properties...", untick the "coding completed" option and click save. Proceed to the next item and repeat as above until the end of the list.
2. To allocate the same 25 items to a third reviewer, you would proceed as usual, on the "collaborate" tab, "Create new" coding assignment and select the same options as for the first two reviewers.
When the third reviewer will have completed this batch you will be able to create a new three-way comparison (if needed) but in your case it would probably be OK to compare the coding only between the new reviewer and the one that had completed the batch (Anne).
I hope this clarifies, please do come back to us if you'll need some more information.
Best wishes,
Sergio