Step 1.) Navigate to Active Directory Users and Computers on a domain controller with access to the user's account that is to be changed.
Step 2.) Locate the user in question for which the GID is to be changed.
Step 3.) Right click on the user and choose "Properties".
Step 4.) Locate the Unix-Enabled tab in the user's properties.
Step 5.) Manually change the GID to a new Group ID
Step 6.) Click "Apply" and "Ok"
The User's Group ID has now successfully been changed, please wait 5-10 minutes for the changes to replicate before logging in with this user.