I want to extrude the vertices but it didn’t appear in the mirror modification
how can I make this missing part appear ??
Hi,
You mean this one?

yes it is.
May you drop your .blend file please?
Nishikigi_mouth.blend (833.4 KB)
Done.
You had double vertices. I had to turn on X-ray mode to delete and re-create them again.
Nishikigi_mouth.blend (831.7 KB)
Cheers,
Sergey
is there anyway to join them without recreation?
sorry, I mean recreation.
What exactly do you mean “without reaction”?
You need to take two vertices then press M and choose At Center, At Cursor or Collapse. In my case I chose “At Center”. That’s how vertices are connecting with each other.
Learn to look at the way vertices are joined.

Most of the vertices in the red area have a yellow line joining them - they are connected. The vertices in the green area are not connected to each other - the lines between them are black.
Blender is showing you the problem - the doubles.
can you explain how you delete it i can’t see that little.
A’ight, hold on a min.
Or simply
Btw these three are in fact 48 vertices. You definitely did something wrong before
Probably extruded the vertices and then canceled 15 times, without undoing the extrusion.