If I understand you:
-You blocked Item ('Blocked' field) on Item Card;
-You gone to another Item Card;
-You want to came back to blocked item and 'unblock' it.
If I described your scenario, you can unblock this field. Have you some customization on Item Card related with this field and what version you use?
I can post picture with this changing to be sure. If your scenario is not as I described, please put us more details.