How to move the registration form on the checkout page?

Question

WordPress

Good day dear!
Faced a problem that I don't know how to solve...
WordPress site, Ocean WP theme. Checkout page.
So it is:

So it should be done:


In a nutshell: make the left side of the form tabs. One input - a form for an unregistered buyer, the second tab to display an authorization form if the buyer is already registered on the site.
I re-picked 2 plugin files: checkout/form-checkout.php and checkout/form-login.php - only everything breaks and the result is zero. Maybe you can at least give me an idea, or if anyone has come across such a task, I will be grateful if you help me implement it.
Many thanks in advance to everyone who responds! :)