Most self employed workers can deduct premiums paid for health insurance, dental, and certain long-term care insurance. This is typically a large deduction, so you should make sure you qualify. To benefit from this deduction, you must not be eligible for an employer sponsored plan, either from your employer or your spouse’s. If you meet that criteria, then you can only deduct as much as you have in business income; so if your business has a loss this would not be available to you. If you have multiple businesses, you cannot combine the income to maximize the deduction, you have to choose one of the businesses to essentially be the health insurance plan sponsor (so choose the one with the highest income).
This deduction is a personal tax deduction, so you take it on Schedule 1 of your Form 1040 (not your schedule C). If your health insurance premium deductions are larger than your business income for the year, if you itemize your taxes you can deduct the excess as an itemized deduction on Schedule A.
One other note, if you had a medical emergency and your health expenditures exceeded 10% of your adjusted gross income (“AGI”), you can deduct anything over 10% on Schedule A of your tax return if you itemize your deductions (this is actually set at 7.5% for 2020, but will revert to 10% in 2021 unless an extension is passed). Note that you can’t double deduct (meaning you can’t deduct your health insurance premiums on Form 1040 and then again on Schedule A).