If you wish to underline the selected text, follow these steps:

1. Highlight the text you wish to underline or if it is the whole content of the text box, select it and click the Underline field from the text editing toolbar.

https://cdn.elev.io/file/uploads/Nx6j1ilgYkjKwwUzxKv9Jx2yWyIGUZG4VbEE9W71H30/xkz9azblz8XShpoxXgZ9EYqZ0NRfonFjmxrYET5Z_Gw/underlining text.fw-Vnc.png

2. Save your page when you're done or continue editing.