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You will want this handbook: http://www.cacities.org/getattachment/724cf4ef-006c-4166-97c5-6e8ecb0e548c/LR-Tort-Claims-Article-REVISED.aspx (it is the California Cities and Municipalities handbook for the tort claims act - this is the handbook used by the cities in reviewing your claim). Information on filing an application for a late claim starts on pdf page 8.
You will want to first contact the city/municipality directly, ask if they have a specific form for a late claim (if they do use it, if not you will have to draft (write) your own).
If you have to write your own, include all of the same information that you had on the original claim (identify the municipality, the location of the accident, etc.), and then include a declaration showing why the late claim should be permitted (include documentation to support it - so a copy of the original claim to the other municipality and the original claim to the correct municipality).
Again, I would review the handbook that I provided above, it gives you the basic legal authorities that the City is going to use when they review your claim, it can help you immensely if you draft your paper using this as a background (understanding what the city is looking for will help you best draft your petition).