In Hostinger Website Builder, you can change the button shape in two ways:

Expand the Website styles panel on the left, open the Buttons tab, and select the preferred button shape (oval, rounded, rectangular):

If you make changes in the global style settings, they are applied to all buttons across your website, including regular buttons, “Add to bag” buttons in single product and product list sections, and submit buttons in contact and subscription forms.

Locally, you can change the button shape for the following elements:

Within the editor, click on a button element and select Edit button. Then, open the Style tab and change the corner radius:

Click on the contact or subscription form and select Edit form. Open the Style tab and select Submit button from the dropdown. Then, change the corner radius:

And that's it!