Navigating by the stars/sun has been pretty settled for hundreds of years. Given accurate timepieces and a sextant it's really straightforward.
I linked you to a manual from 1804 that shows how to do this in a previous thread.
Given that the sun is visible most of the day that time of year, you can just use a 24 hour watch, point the hour hand at the sun, and 24 o'clock will point along a consistent meridian depending on what timezone you have set on your watch.
Of course, a modern traveller would just use GPS, but either way you get where you want to go.
Edited because I clicked "post" too soon, added this:
---
So it's not a definite proof that, on a Monopole model Flat Earth, that they ventured out into the infinite plane.
Doesn't matter - what matters is that YOU CAN GO TO ANTARCTICA AND GO OVER ANY ROUTE YOU WANT, you just have to be able to pay, and you better be in good shape and know your way around survival equipment.
The context of this conversation was assertions that people can't go to Antarctica.
You can go. You can test whatever theory you want there.