Ive already filed. I then received a schedule K1 that was not included in my return. How do I amend?

If you have already filed your returns and they have been Accepted, you will need to wait until the IRS fully processes your return and you receive your refund. 

Next, you will need to Amend your Tax Return by filing Form 1040-X to include the information from your K-1.  

You can click here for instructions on Amending your tax return:  How to Change a Tax Return You Already Filed.  TurboTax will walk you through Amending your State Tax as well.