Hi there!
Thanks for reaching out.
You can go to .../language/en-GB/en-GB.com_sppagebuilder.ini and open it using your text editor like Sublime Text or Atom.
Find and Replace your text in this following code.
; Ajax Contact
COM_SPPAGEBUILDER_ADDON_AJAX_CONTACT_NAME="Name"
COM_SPPAGEBUILDER_ADDON_AJAX_CONTACT_EMAIL="Email"
COM_SPPAGEBUILDER_ADDON_AJAX_CONTACT_SUBJECT="Subject"
COM_SPPAGEBUILDER_ADDON_AJAX_CONTACT_MESSAGE="Message"
COM_SPPAGEBUILDER_ADDON_AJAX_CONTACT_SEND="Send Message"
COM_SPPAGEBUILDER_ADDON_AJAX_CONTACT_SUCCESS="Email sent successfully!"
COM_SPPAGEBUILDER_ADDON_AJAX_CONTACT_FAILED="Email sent failed.
Screenshot: https://share.cleanshot.com/WBK0xpzz
If you have any ready Joomla module to use, then you can integrate the Joomla module in a SPPB page using the Joomla module addon.
Best Regards