I'm converting 4t2 with the permission of the original author.
The whole process is perfect
But the mesh of the shoulder area and armpit area is curved
How should I solve it?
The picture is an example

Not entirely sure what you mean by the area being curved. I'd guess it's either an issue that stems from having to move the arms into the correct position before converting (TS3/4 meshes have arms lower than TS2's arms in the T-pose, which can affect the conversion a little bit), or from bad joint assigning in the area (could need either a different base mesh for the auto assigning, or some manual adjustments). Could also be a few other things, but those are most likely.

Can you show on your conversion of the mesh, or alternatively post the mesh file?

I modified the joint yesterday
I solve it!!! Thank you!!