You'd essentially prorate your maximum contribution by the number of months you had coverage. The maximum contribution is $4,150 for Self coverage or $8,300 for Family coverage, plus an additional $1,000 if you're 55 or older. You're considered to have coverage for each month that you were covered on the first day.
So if your coverage started May 1, you'd be covered for 8 months for 2024, or 75% of the year. Multiply that 75% by your max contribution and you'll have the amount to include on line 3.
