The NewsletterForm Plugin by ContactUs.com, allows implementing a default tab + form combination on your website, or making a custom implementation on every page of your website, as well as selecting a different template for your tab or Embeded Form version of the contact form.
If you want to fully customize your Newsletter Form, e.g. customize the text, the tab color, the call out button message, and more, this needs to be done in the admin panel, but there's a shortcut to get there from the plugin. On the (1)Forms tab, click on (2)Design and then select to (3)Edit Form Design or Edit Tab Design.
Notice that you have these options per Newsletter Form so you can easily go into the settings of each one.
Once you click on Edit Form Design, you'll be redirected to your form's settings page in your admin panel. This section shows the Embeded Form template you have set up, and gives you access to all customization features. To customize/configure your newsletter form, hit on each tab to change the specific settings that you need. Each tab allows customizing different sections of your contact form, such as business information, additional settings such as enabling international phone numbers, and more.
Once you click on Edit Tab Design, you'll be redirected to your form's triggers tab.This is how the Form Triggers tab looks like. From here, you can customize your tab, set the tab position, change the tooltip settings and much more.
Once you have finished configuring every section, save and publish your settings. Go back to the plugin, select your implementation, e.g. tab version or Embeded Form version, save the settings and the form will go live.
Here is a helpful video that will help you with the form configuration.