If you want to delete a CSN card registered for a user and reuse it you can follow the procedure below.
1. Delete the card assigned to the user by clicking on the trash can.
2. Select the user you want to assign the card.
3. Click +Card.
4. On Registration Option click Assign Card.
5. Enter the first numbers of the CSN card and search.
6. Select the card.
7. Click Enroll.
8. Click Apply to assign it to the user.
Versions Before BioStar 2.6
Unfortunately Wiegand cards cannot be searched with Registration Option : Assign Card until BioStar version 2.6.
The best way to assign a deleted used Wiegand card to another user would be to use the .csv import feature.
Refer to the KB article to understand how to import a user with CSV: How to export and import users
You can search a unassigned Wiegand card in BioStar 2.6 but you have to enter the full wiegand ID with the FC and the card ID.
For instance, with the card below the search will fail if I only enter 12-3.
I will have to enter all 12-34567 before pressing the search button to search the card.