The Fund should have provided a tax supplement info that shows how much (percentage) of the dividends were from each of the 50 states.. So in that provided table you could pick out your resident state's percentage (and/or non-resident/PY resident state), and lump all the others as "multiple states." If the Fund didn't send you the supplementary material, you can usually find it on the Fund's website (or brokerage) in their tax info section.
When entering into TurboTax, when that followup question is asked, one of the choices for state is "Multiple states." As an example, if you have only 1 state return, you could report 2 "states"--the amount for your resident state and the total of all the other states as "multiple states." If you're preparing returns for more than one state (such as an additional non-resident or part-year resident state) and need to show the dividends from those additional states, you could make a third entry, or fourth entry, etc. , using "multiple states" for the total of the rest.
@ SteamTrain
Do you have anything else to add here? Thanks.