Step 1: Kindly go to AD Mgmt --> User Management --> Bulk User Modification --> Enable/Disable Users.
Step 2: Please specify date you want to set for your contract employee from Account Expires.
Now, to specify the contract employees you can,
a. Import a simple CSV file with the sAMAccountName of the users. The users will be matched and displayed. You can then click on Check All and Apply this change.
b. Click on search and it will give you all the users in your domain. You can handpick users and apply this change.
c. If all the users belong to an OU, you can choose the OU on Add OUs and hit Search. All users from that OU would appear. You can then click on Check All and Apply this change.