If you already filed, you will need to amend to add it after you receive your refund. If you have already e-filed or mailed the return, you will need to wait until the IRS has accepted or rejected that return.
After you have received your refund, you can go here and get instructions https://ttlc.intuit.com/questions/3061514 for amending that return.
And you can follow these steps to get to that portion of the interview to enter your K-1.
See some reasons you'd need to amend your return here https://ttlc.intuit.com/questions/1908543