AAA Form Builder gives you the option to send an autoresponder email to the person who fills your form. Follow the steps for guidance –
Step 1. Log in to your Shopify store and navigate to Apps > Form Builder.
Step 2. Create or edit a custom form.
Step 3. Navigate to Form Settings -> Emails -> Thank You Email Settings
Step 4. Toggle Reply Email field to Enable
Step 5. Customize the email as per your need. You can specify Reply To Email, edit the email Subject and Body
User Email Template Background Color option to enable/disable the email background color.
Step 6. Once you are done customizing your email, click on the Save button