Incorrect.
Changing the Rules of the Senate requires a majority vote of the members. That is 51 votes. They can dismiss the impeachment with that backing.
McConnell may already have enough votes to do it. If so, he should proceed.
It takes a 2/3 vote of the Senators present to convict and remove the President. That could be 10 Democrat Senators, hanging around during a lunch hour, while everybody else left, if the Republicans were foolish enough to allow such a condition.
I would expect the Republicans are not quite that foolish.
You can bet that the Democrats have discussed a similar plan as a long-shot measure.
I could be wrong, this is part of the more arcane set of rules. I believe the parliamentarian says 2/3 rds vote for a rules change but can be overridden by a simple majority. This is murkey because the rules may not already cover this circumstance...because when they made the rules, they were reasonably close to sane.
DK