Calculating withholdings with Federal insurance premium assistance

Hello,

I had approx $500 (over 600 once I paid TurboTax to file because I used the 1099-A) surprise in my last taxes.

I was getting help from the federal government to pay medical and dental insurance premiums (cancelled them after this surprise as it almost ruined me). I think adjusting my withholdings will help but I don't know how much to withhold. I've tried calculators but I just get lost... I want to prepare better for next year so I can get insurance again without destroying my life financially.

How do I calculate how much withholdings to do to avoid paying a large amount in taxes thanks to this assistance with insurance premiums? (Where do I put the federal premium assistance credit amount in a withholdings calculator? Do I put the monthly or yearly amount? This is where I get lost in calculators like on the IRS site)