You can't amend your Schedule C into a Form 1065. You need to prepare your Form 1065 using TurboTax Business. You will then amend your Personal Return to delete Schedule C and the K-1 that will be generated when you create the Form 1065. The Form 1065 has to be done first, as it is necessary for your personal return.
For detailed on information on how to amend see the following FAQ: https://ttlc.intuit.com/replies/3288565
