How do I "tie back" my schedule C self-employed income to my 1095-A marketplace insurance so I can deduct it?

When you enter the 1095-A there should be a box to select  "Self-employed and bought a Marketplace plan".  It will automatically include those premiums in the SE Health Insurance section. So you shouldn't enter it again on schedule C.

Self-employed health insurance deduction goes on Schedule 1 line 17 (which goes to 1040 line 10), as long as the expense is not greater than your net self-employment income. If it does exceed your net self-employment income it gets split automatically. An amount equal to your net self-employment income goes on Schedule 1 and the remainder gets added in to medical expenses on Schedule A. It will not reduce any SE Tax on a net profit. It just reduces your AGI.