Here's how to file two part-year resident returns in TurboTax:
https://ttlc.intuit.com/community/state-taxes/help/how-do-i-file-a-part-year-state-return/00/26057
Your fiance became a resident of GA for tax purposes (and ceased being a resident of MI) on the day he began living in his new home in GA. All his income from that date forward is taxable by GA. As @xmasbaby0 stated, his DL and license plates are irrelevant to determining his residency for tax purposes.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
