My friend fell and broke her foot would like to put the establishment on notice via thier insurance carrier, how do I proceed and what do I write?

First, you can call the establishment and ask them for their insurance information to attempt to expedite the process. If they do not provide it, send a letter via certified and regular mail, giving a brief description of the accident, and asking them to contact you and provide their insurance information. Include a self-addressed stamped envelope addressed to your friend. Parenthetically, it would probably be better for your friend to call and write the letter in her name, since it is her claim.