If you perform services for an LLC and receive a K1, the Self-Employment tax is generated from Box 4 (guaranteed payments for services) and/ or Box 14 A - net income from Self-Employment. These figures produce self-employment tax on Schedule SE. You do not pay into the SE tax (Social security, Medicare) by adding a Schedule C on your tax return. So, you would only enter your K1.
If your K1 has nothing in Box 14A or 4, and there's a positive amount in Box 1, your K1 may have been prepared incorrectly. Talk to the accountant and ask why your share of the income has not been reported as services- based.
