I don't think you understand the basics. An LLC is a legal entity that you set up. It is not a tax entity. Once you have an LLC, if you don't do anything else, you are disregarded. As a sole proprietor, it becomes a Sch C business as part of your tax return. If you have others in the LLC with you, it becomes a partnership and you file a 1065.
You mentioned S corp- to be an S corp, you have to send Form 2553 to the IRS electing to be treated as an S corp. See S corporations | Internal Revenue Service. If you are an S-corp and have an EIN, the company you worked for would not send a 1099.
Since you got a 1099, either the employer believes you are disregarded or you didn't give them the EIN of the S corp.
My guess is that you are a sch C, it is part of your tax return.
Add the business to your return and put the income as part of the business.
See Tax information for businesses
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