No, don't enter $0. If the IRS adjusted your refund from your first filing, that means their records show that you received those payments.
Since you are adding two dependents, you will only receive the stimulus amount for those dependents (if you did not already receive it).
You don't need to calculate what you 'should receive', the IRS will figure that out. Just enter the amount you actually received.
Click this link for more info on the My Refund was Adjusted for the Recovery Rebate Credit.