HOW can I remove this well/pit distortion effect?

The links to your sound samples say “Error 403 Forbidden”.

Possibly the WAV is mid/side rather than right/left.

MSED suggested settings.png
There is an Audacity-specific mid-side decoder plugin …

Alternatively, a simple solution: split the stereo track to two mono tracks & delete the left (the upper) track
Then you will only have the centre track as a mono, (not stereo), recording, (i.e. stereo is sacrificed in this simple method).

Abandoning the side channel is the easiest way to eliminate the abnormal wide stereo-effect …

abandon side, centre only.gif
This will also reduce, but won’t completely remove, the reverb(eration) from the room.
[There are de-reverb plugin$, but IMO they are only of use in mild cases, and are expensive].

Most of the reverb is in the bass frequencies, so cutting the bass will reduce the reverb

Apparently 2 mics: one top, one bottom …

If one end pointed towards you that will be middle, the other mic side.
For audiobooks one mic is usual, (IMO just delete the side channel).

Your recording space is resonant / reverberant. :frowning:
Treating the space/ surfaces with sound absorbing material is better that trying to fix it in Audacity.