Example of how to filter the ticket selector button text to change 'View Event Cart'.

functions.php

<?php //Please do not include the opening PHP tag if you already have one.

function tw_ee_custom_filter_ticket_selector_submit_button_text( $btn_text, $event ) {
	
	if( $btn_text === 'View Event Cart' ) {
		$btn_text = 'Add/View Event Cart';
	}
	return $btn_text;
}
add_filter( 'FHEE__EE_Ticket_Selector__display_ticket_selector_submit__btn_text', 'tw_ee_custom_filter_ticket_selector_submit_button_text', 15, 2 );

Reference:

https://eventespresso.com/topic/changing-the-text-once-an-event-is-added-to-the-cart-using-tables/