I don't understand your question.
Your MI state itemized deduction form lines 3a-3c calculates your state itemized deduction for taxes paid. You can't deduct MI state income tax on your MI state return. So line 3a asks for your total federal SALT deduction. Line 3b asks you to list MI state income taxes. Line 3c is your allowable MI SALT deduction.
For example, suppose on your federal return you deducted income tax from two states, say Mississippi and Alabama, because you worked in both states. And you deducted some property taxes. Your MI state income tax is not deductible in MI, so this calculation takes your federal deduction, substrates the state deduction for MI income tax, which allows you to deduct your AL income tax and your property tax on your MI state return.
I don't see any "credit" or any adjustment for the fact that you might have paid more than $10,000 of state taxes and be limited by the cap.
