The City of Detroit doesn’t appear to require the filing of
a Michigan state income tax return when amending your city return.
And, since you just want to file a part-year resident income tax
return instead of the resident income tax return you originally filed, there
shouldn’t be a need to amend your state return.
You’d want to amend your state and federal returns if you had additional
income to report, but based on what you’re saying, you're just changing residency status.
Instructions can be found at Detroit’s 2017
City Individual Income Tax Forms page.
