Hello @SmartCaregiver

To make tagline bigger you need to add custom CSS.
For this you need to go to Admin Panel / Appearance / Customize / Theme Options / Advanced Options.
Here you need to copy and paste below CSS:

p.site-description {
    font-size: 20px;
}

Note: Change to value 20 to your size.
Hope this will help to resolve your issue.

Regards!!!