To edit the Submit button, go to your Form Editor and click on the Submit button area. Its Edit Field panel will open on the left side of the page.
There, you can change the text displayed on the Submit button and its alignment.
If you want to customize the button in terms of appearance, you can achieve this by going to the Show Theme Options button in the top right corner of the form right next to the preview button.
How to align the Submit button?
How to redirect users to other web pages on submit?