I’d like to have 2 forms in my calculator. The 1st one is a contact form.
The 2nd is a booking form. The button to open the booking form should appear once the contact form is submitted 
In the success message (Your submission has been successfully sent.), use the code editor to add the buttoncode that opens your booking form to the text field.
I haven’t tested it, but it should work.
@Sina, thank you so much for your note!
@Resultat_Grabbarna, Sina is right! As a workaround you can add a custom button to the Success Message that will redirect your clients to the booking page on click.
To achieve this, just open the Code Editor mode for the Success Message field and paste the button code there. Here is an example of the code:
<button style="background:#ff6b35; color:white; border:none; padding:12px 30px; font-size:18px; border-radius:50px; cursor:pointer; font-weight:bold" onclick="window.open('https://example.com', '_blank')">
Book Now
</button>
Feel free to adust the button text, link and styling to your needs 