@IntuitAustin or @IntuitBettyJo will quickly get these broken links fixed https://proconnect.intuit.com/community/help-articles/help/form-1045-application-for-tentative-refun...

then all will be clear to you. Especially this one. Intuit's primary mission is to be helpful to all users, that is why they have the FAQ's in the software. On very rare occasions, those links get modified and lost. This seems to be one of those. I would love to rewrite what they had there, but they did such a great job I would hate to not do it justice. 

The only hint I will offer at this point is if you are working in the 1040, Screen 60. In the Refund section, there is an Add. That opens up 3 more years for a total of 6 to do the carryback with.  See images

1st 3 years 

Then after clicking Add the next two years