Help for canonical URL

A friend of mine has a blog and he added recently a membership premium area. He asked me if I could help him with taking care of problem shown in AHREF's Site Audit but I noticed a lot of errors: basically, 140 Pages with the critical problem of the wrong canonical URL( I mean, in fact he doesn't set It up, so technically there isn't any canonical URL), and every Page of the website's area where you need to login in order to read Is seen by AHREF as a duplicate of the login Page, because also the page's URL of the membership are "https://www.(namewebsite).com/wp-login/(name of the Page with premium content)", so It all redirect before to the login Page. Do I have to set 140 canonical URL or there Is a more clever and faster way to fix this?