You need to amend the Grand Rapids return you previously
submitted. To amend the return and request
your refund, you need to complete Form GR-1040X, Grand Rapids Amended Income
Tax Return. See the “1040 Amended” link
at the Grand Rapids Income
Tax Guide for Individuals page.
Not that amended returns cannot be electronically-filed for
Grand Rapids; they must be mailed to the address specified in the instructions.