How to change the tagline “Just another WordPress site” in WordPress
The default tagline “Just another WordPress site” is displayed on the front end of your WordPress site under the site title. You can change the text to whatever you like.
After you’ve logged in go to Settings menu>General submenu, enter the desired tagline in the Tagline field and click on the Save Changes button at the bottom of the page. You can also make these changes from your theme setting.
Go to Appearance menu>Themes submenu>Customize button for the theme > Site Title & Tagline panel on the left hand.
If you made changes through the theme setting, it will change the general tagline setting as well.