Hi Abey,
You can follow the solution regarding the same issue here.
If you prefer to use a different plugin to display the pop-up after submitting the form, you may try the “Popup Maker – Popup for opt-ins, lead gen, & more” plugin.
You can follow their official guideline from a support ticket to trigger the pop-up after submitting the form here.
Give it a try, and let me know how that goes! 