One of the sections within the Know Your Client area of contact overviews is the Estimated Tax Information section, accessible by clicking the "Financials" tab at the top of this section:
To add or edit any information here, click the Edit button in the top right corner of the section. You'd then see the below:
Enter the client's AGI, Estimated Taxes, whether or not the data is confirmed by a Tax Return, the Tax Year and the Tax Bracket here and this section will look similar to our original example above, based upon your numbers.
Note: Adjusted Gross Income and Estimated Taxes are fields that you can include in any Custom Exports you build.