Vhanging the behavior after clicking on the sticky button

I want the button redirection to be directly at the checkout page ….
In other words:
When the customer enters a product page and sees the sticky button and clicks on it, he is directly redirected to the checkout page (payment page)
In short, I want the button to be “Buy now” and not “add to cart” …
Thanks for answering me ASAP
Have a good day