The solution (from Pablo Escobedo) for Divi 2.4+ is to edit the following code in;
change Submit here for whatever you like:

esc_url( get_permalink( get_the_ID() ) ),
( 'on' === $captcha ? $et_pb_captcha : '' ),
esc_html__( 'Submit', 'et_builder' ),

*** This code below is for pre Divi 2.4+ ****

To change the text in the submit button on Divi Contact form you need to edit the funcions.php

Best way to do this is to use a child theme, then copy functions.php into the child theme folder

Then find the following code and edit the SUBMIT text to your new button text

( isset( $_POST[‘et_pb_contact_message’] ) ? esc_attr( $_POST[‘et_pb_contact_message’] ) : $message_label ),
__( ‘Submit‘, ‘Divi’ ),

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