Redirect the form back to my website after successful donation

Right now, form redirects to a "Thank You for your submission" following donation. I am unable to put a condition for after paypal submission.  Please advise if this is possible.

Condition isn't what you need. You just have to define your custom thank you URL in your form.

Here's how:

In the bottom part of your form, click EDIT THANK YOU PAGE then enter a redirect URL (your thank you URL)