How do I pay back to my heath plan?

Are you talking about marketplace health insurance?   Did you enter a 1095A?   If you owe for that, it is included as part of your federal tax due on line 37 of your Form 1040.  Or it might just be reducing your refund.

If you had health insurance from the marketplace, when you applied for the insurance, you gave healthcare.gov an estimate of how much income you would receive in 2024.  They used that amount to calculate how much of the insurance premium would be covered by the tax credit and how much would be your amount to pay.   So...you had some monthly amounts to pay, and the rest of the cost of having that insurance was paid by the government program.

If you ended up making a higher income than you told them you would receive, they re-calculate how much should have been paid by the program and how much should have been paid by you.   And if your own share of the cost should have been more, they get it back on your income tax return.   It will be part of the "tax due" amount on your Form 1040 or it will reduce your refund.

If you actually had less income, you could even get some of the share you paid back on your tax return.