The following batch solves your need:
@Echo Off
:: XRen.bat Syntax: XRen [Unit:]PathName
If exist %1.\Nul GoTo EXEC
Echo.
Echo Direwctory %1 not found
GoTo EXIT
:EXEC
Dir %1 /B | Find "[1]" > %0.tmp
For /F "tokens=1,3 delims=[]" %%A in (%0.tmp) Do Ren %1\%%A[1]%%B %%A%%B
If exist %0.tmp Del %0.tmp
:EXIT
Save the batch in your root (C:) directory and run it from the Dos prompt in a Dos window (in fact in a DOS emulated machine, NTVDM under Windows NT) typing
XRen PathName of the directory where the [1] files are stored (e.g. XREN C:\MyDir\Myfiles).
Avoid names containig spaces if so get the dos format name using a dir /X command.
Repeat the process in each directory where there are files to be renamed.
Good work