The Shack Forms button used to send a form by default displays "Send" text:

This text most likely will be a good fit for the majority of sites. If it is not a case with your site, you can customize the Send button to use your own custom text.

• Open your required Shack Form.
• Click the Theme tab:

• Scroll down to the Fields options group of settings.
• Locate the Send button label parameter.
• Enter your preferred text into this field. In my demonstration, I entered "Submit Your Form!".
• Click Save or Save & Close:

• Now check your form's button at the site front end. You should see your custom text at work: