How did gordian untie the knot?

just loosen it

The Gordian Knot of history was a complicated Turk's Head, tied with the bark of the Cornel Tree. Over time, the bark shrank and hardened, making it impossible to untie. Many tried, and ALL failed....

There are no evidence of that.

First you will have to un-weave the short- or long-splice just above the Monkey's Fist. Most sailors just cut the rope right there, on the short side of the splice. After that, it will unravel pretty...

It was said to be impossible to be untied -and so it was cut asunder by sword, using 'the Alexandrian solution' -a bold stroke!