On June 10th CNN posted an article saying "President Donald Trump's campaign is demanding CNN retract and apologize for a recent poll that showed him well behind presumptive Democratic presidential nominee Joe Biden. The demand, coming in the form of a cease and desist letter to CNN President Jeff Zucker that contained numerous incorrect and misleading claims, was immediately rejected by the network. 'We stand by our poll,' said Matt Dornic, a CNN spokesman."
The letter came in the form a cease and desist, and was signed by the Trump campaign's senior legal adviser Jenna Ellis and chief operating officer Michael Glassner, demanding a "full, fair, and conspicuous retraction, apology, and clarification to correct its misleading conclusions."
A semi-exhaustive Google search turns up no results for any legal action by the Trump Campaign against CNN related specifically to this poll. It is unclear why there was no follow up as of this point nearly two months later.