Here are the steps to add a question to an existing section in your Microsoft Forms form:

1. Sign in to Microsoft Forms.
2. Choose the form you want to edit.
3. Select Add to add a new question or section.
4. Type your new question and answer options.
5. You can also add a picture or video to your question.
6. To add it to an existing section, select the Add to an existing section drop-down arrow.
7. Choose the section to add the question to and select Add.