To review Schedule O Supplemental Information to Form 990 or 990-EZ:

1. From within your TaxAct return (Desktop), click Federal. On smaller devices, click in the upper left-hand corner, then click Federal.
2. Click Schedules in the Federal Quick Q&A Topics menu to expand, then click Schedule O - Supplemental Information to Form 990 or 990-EZ.
3. Continue with the interview process to enter all of the appropriate information.

Per IRS Instructions for Form 990 Return of Organization Exempt From Income Tax:

On page 4:

C. Sequencing List To Complete the Form and Schedules

In general, first complete the core form, and then complete alphabetically Schedules A–N and Schedule R, except as provided below.

On page 83:

Appendix E. Group Returns—Reporting Information on Behalf of the Group

In general, if a line requires a Yes/No answer and the answer isn't the same for all subordinate organizations to which the line applies, then check “Yes,” and explain the answer in the schedule's supplemental information section (if applicable) or in Schedule O (Form 990 or 990-EZ).

Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.