not sure what you mean by using a “social login for placing order”
if you mean using a social login widget of some sort to login then i am sure there are many plugins out there that let you add a login widget of that sort whereever you want it to be

if you want it to replace the login provided by wppizza on the orderpage,
you could add a widget (presumably via some shortcode) using the

wppizza_order_form_before action hook and – probably – remove the wppizza login form by running a

remove_action( ‘wppizza_order_form_before’ , ‘wppizza_do_login_form’ );

or some such

>but want also to have support for social login if possible?
then you have to add a social login widget somewhere

wherever you want to put it ….
i really don’t understand the question here