split path and take last folder name in batch script

@echo off

set MYDIR=C:\FOLDER1\FOLDER2\FOLDER3\
if "%MYDIR:~-1%" == "\" set "MYDIR1=%MYDIR:~0,-1%"

for %%f in ("%MYDIR1%") do set "myfolder=%%~nxf"
echo %myfolder%

outputs

FOLDER3