Cannot tighten the screw?
There was a case the screw at the bottom of steering unit became loose and undone.
In this photo, there is a gap between 2 yellow layers on the red-circle side. The screw may not be engaging at all.
Why is the screw not engaging?
The reason is, these 2 yellow frame layers have gone out of line. The screw is not going into the 2nd layer at all. The screw is not engaged to the thread on yellow part side. This video explains.
What to do
1) Loosen the other screw (which is tight at the moment, unlike the other screw) in order to give some absorbance so that the 2 yellow layers will able to move to right position (Do not completely take them off ).
2) Find the right position of 2 layers (youtu.be/tSuVGkRGHN8?t=53)
3) Tighten the screw (which was loose).
If it still does not work,
Loosen (only loosen, instead of taking them off) the 2 screws on the other (right/left) side, too,
so that the absorbance will be even wider.
Out of 2 screw points, the one close to another small screw (white arrow in the photo) is much easier to make it right. So, leave this point without a screw and start with the other (Green arrow in the photo)