How to Change the Site’s Title and Tagline in Multi WordPress Theme?
To change your site’s title, from your WordPress Dashboard go to Appearance > Customize > Site Identity and use the Site Title option.
You can edit the site’s tagline there as well. In Customize > Site Identity, just below the page title, you can see the tagline and edit it.
You can also choose to hide both of them. Just untick the Display Site Title and Tagline box below.