First time filing this form. My on-site CPA passed away in early February. This is way over my head.

1099-S Box 1: 04/03/2023 Box 2:$1,000,000 Box 6: $1,436.33 

On Schedule D Part II I have:

Proceeds $1,000,000

Cost (or other basis) $3,000 because he paid $3,000 to install a new septic tank

Gain is calculated at $290,457.

He owes IRS $46,572

If I exclude the $1,000,000 sale proceeds his taxable income would be $60,531.

I am contacting CPA firms to see if they would be able to review this for me as I am nervous now. I am a CPA student but this is over my head. 

Any help is appreciated.