I do it at this website https://www.annualcreditreport.com/cra/index.jsp

I remember the credit angency you selected asked you to create a username and password.  I guess you use that to check back in 30 days.  (I always printed the reports out and file them.  I'm obssessed with filing papers. )

If you have checked with a particular credit agency in the past 365 days, they will tell you if you select that agency again. Then you can just move on to the next one on the page.