There are many free affiliate program for Prestashop 1.7 like Luzkoviny.
I have used Sendinblue. They offer the affiliates almost for free. They are a platform where bloggers can meet the parties interested in helping them sell the product.
Apart from that, I know about All-in-one-rewards. They are one of the best as well.
They are not as good as Sendinblue but they are ahead of the most of the curve.