You can change the instant booking button text from your HomeRunner settings. No code edits are needed.
Property page booking widget. Go to HomeRunner > Settings > Booking Widget and edit Instant booking button text. The default value is "Instant Booking".
Checkout page submit button. Go to HomeRunner > Settings > Reservation and edit Instant booking button text. The default value is "Confirm & Continue".
After saving, do a hard refresh to see the change.