Adding HTML to my sites Title

The suggested way of making changes to a theme is to first create a child theme. Then you would modify a copy of whichever file pertains to the part that you want to change. For example, if you want to add LLC to the end of the company name in the footer, then you want to copy footer.php from the parent theme folder into your child theme’s folder and make the change there. Likewise, make your changes to a copy of header.php in your child theme if you want to make changes in the header. Don’t make changes to the parent theme’s files, as those changes will be lost when/if the theme gets upgraded/updated.