An H1 tag can be added to each Master Layout on the website which will cause each page to have an H1.

To add an H1 tag to a Master Layout:
  1. Navigate to onMessage > Website > Mainsite > Master Layouts
  2. Select the name to edit a layout
  3. Insert a text block in a non-obstructing location
  4. On the Text block, from the select Category drop down, click + Create New 
  5. Title your text
  6. Click Save & Close
  7. Click the pencil icon to edit the Text
  8. Select HTML in the top left corner to edit the HTML
  9. Enter <h1></h1>
  10. Click Update
  11. Click Apply Changes