It's not just related to Reputation Bar.
Basically, you have to obtain a minimum of 5 points. You can obtain these points by some events in ME2 and some in ME3.
I don't remember them all by heart, but if you did Tali's loyalty mission in ME2 and proved her innocence, that's 2 points. If you did Legion's loyalty mission and took the...destroy? option, I think (maybe it was rewrite), you get 2 points there as well. If you solved the Legion/Tali conflict, 1 point.
In ME3, if you go save Admiral Whathisname on the planet, and insist on rescuing him, that's 1 point. If you do Legion virtual reality mission, 1 point. And there's another event worth 2 point that I don't remember right now.
Here's the link for a handy flowchart of that, though it's missing some ME3 options. Pretty sure Legion's virtual reality also gives point.
Here it is