Redirection of a URL

My website has 2 pages with URLs like https://example.com/product/1/ and https://example.com/product/20.

Both pages show the same products, so I deleted one page. So I have only one page with URL say,https://example.com/product/20.

But the other page ranking 1st in SERP, so how can redirect it to the other page? What can I do? Please suggest? How to do it, if it with 301 redirections?