And how are they supposed to "recognize their own biases and consider how they affect their coverage"?
What are they supposed to do about it? Answer me that.
Well, first, they could go back and watch their own segments and possibly notice that, say, when single-payer health insurance comes up, they ask, "How are you going to pay for that?" but not when, say, invading other countries comes up.
They could also seek out criticism of their segments and consider whether their critics might have a point.
EDIT:
Don't tell me there's no media bias against Bernie Sanders, especially considering that he's well ahead in polling of all but two of those candidates (Biden and Warren being ahead of him).
EDIT #2: And notice that Andrew Yang (per RCP, 7th overall and T7th in Iowa) is left out.