how to center align the submit button in HTML Code

By default the submit button is centered already in your form.

I have checked the form in your account and the submit button is already centered.

Please note that we can only use CSS in the form to edit the submit button.

https://www.jotform.com/help/117-how-to-inject-custom-css-codes

Hope this information helps.

If you have further questions, let us know.