1. Go to Appearance > Widgets
2. At the header widget, insert a “Column” block and choose 33 / 33 / 33
3. As the first block inside your column block, add a “Heading” block and write in the headline.
4. Add any other content below you want inside the column, for example a paragraph:
5. Click the blue Update button in the top right corner.
The result will look like this: