Change first line of bank checkout

-- HikaShop version -- : 4.3.0
-- Joomla version -- : 3.9

For the bank checkout I want to change the first line in terms of font, now I had been messing around a bit but not getting the desired result.
Only the first line should be different something like <h2> for example.

I am not sure where to insert it, namely.

too little experience

<?php echo JText::_('ORDER_IS_COMPLETE').'<br/>'.