You get that info from your mutual fund company. If they did not provide a breakdown, select More than one state at the bottom of the state list.
Fidelity will provide a breakdown...but it's not ready yet.
Eventually, when it does become ready, you will get that info here:
Fidelity Mutual Fund Tax Information - Fidelity
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Even so, unless you had a significant $$ amount that came from your own resident state....the suggested selection of "More than one state" is easiest and always acceptable.
IF you do decide you want to break it down, you have to calculate, on your own, the exact $$ amount that came from your own state, and any US territories.....and you have to do that separately for every bond fund you own. The remainder is totaled together as More than One state....i.e. you don't list every state.
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Example: $1000 in tax exempt interest from a bond fund, and the bond fund says 2% came from your state. SO breaking that down, $20 from your state and $980 from more than one state. If your state taxes at 5%, you saved $1 of state taxes for your effort. Big Whoop !
Other Cautions: Illinois doesn't allow you to do the break out from Mutual funds...only from individual bonds you own. CA and MN have severe restrictions on when a breakout is allowed for Mutual Bond funds...essentially you would have to hold a CA- or MN-specific bond fund.