Comey has already refuted Trump's claim that Trump Tower was wiretapped.
That's not entirely accurate. Trump never claimed that Trump Tower was wiretapped. Trump claimed, very specifically, that President Obama himself had tapped or ordered to be tapped Trump's wires in Trump Tower. "Obama had my "wires tapped" in Trump Tower."
James Comey, being, you know, the cooler cucumber that he is, chose his words very, very carefully when he said, "We have no evidence to support the president's tweets."
Comey was asked essentially the same question three times, phrased differently each time, and he responded each time, very carefully, with the same, exact phrase. He was then asked if anyone at Trump Tower was wiretapped, and he gave the same answer again, explicitly referring to his previous answer.
Now, if you want to take the position that what Trump
really meant was, that someone in the Obama administration wiretapped people associated with the Trump transition team at Trump Tower, then you have to also allow that what Trump
really meant by "wiretapping" was that someone in the Obama administration intercepted electronic communications of Trump and/or his team while at Trump Tower. But in either case, Comey was very careful to neither refute nor affirm either of those characterizations, and instead stuck with the explicit verbosity of the Tweets.
Saying that Comey refuted Trump's claim that Trump Tower was wiretapped is reminiscent of Oregon Senator Ron Wyden's comment on the Senate floor that it was
"established fact" that
"Trump actively encouraged Russians and Wikileaks to attack our democracy" since Trump
"urged the Russians to hack his opponent [Hillary's emails]."
The fact is, Trump didn't do any of that. Trump once joked in a campaign speech that maybe the Russians could find Hillary's deleted 33,000 emails. If you're anti-Trump it becomes conveniently advantageous to spin that as Trump doing something he really didn't do, in the same way that it's conveniently advantageous to spin it as Comey refuted a claim that Trump never made.