It depends. If your W-2 is accurate, you will not need to manually enter allocation amounts. TurboTax will handle it for you. However, if it is not defined, you will need to have a Massachusetts line on your W-2, and then divide 39 by 366 (not 305. California taxes all of your income.) Use this percentage to multiply by your total income. This is the Massachusetts allocation. In the Massachusetts return you enter the "Non-Massachusetts Portion", which is the remainder.
You do want to prepare the Mass return first. California will give you a credit for the tax you must pay to MA on the income earned there.
The box in the screenshot below shows where you can enter the amount in the MA return:
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