Align subscribe button

Hey guys! I hope you can help me. it’s a rather simply issue, but what I need to do is align the contact form on my website. It’s the contact form 7 plugin.

here’s a screenshot of it not being aligned properly https://snipboard.io/acUfFq.jpg

and apparently all I need to do is put in a html code to center it, but I don’t exactly know how to do that. if you can help me with this simple issue that would be very much appreciated!

thanks!