Open Goto Anything or Goto Line (accessible from the Goto menu, if you are not using keyboard shortcuts).
Type ::N where N is the Nth character in the file that you want to go to.
i.e. precede the number with 2 colons.
(Goto Line will prefill one :, so you only have to type one more. Alternatively, you could create a keybinding to execute command show_overlay with the following args, to prefill 2 colons: {"overlay": "goto", "text": "::"})
Alternatively, use the Find panel to search for the following regex:
\A[\s\S]{N-1}\K
replacing N-1 with the desired character number minus 1.
\Aanchor from the beginning of the file[\s\S]any whitespace or non-whitespace character{N}match the previous character class N times i.e.{99}times so you end up with the caret immediately to the left of the 100th character\Kclear what has matched so far