Extract the zip file.open the 2.3x/2.x folder.Upload admin folder to your server from the "Upload" folder.
Upload the install.ocmod.xml file from Extension Installer.
Refresh the Modifications from Extensions > Modifications.
Then Go to Extensions > Modules.You will see the Split Orders Settings.Click on Intall.
After successful install You can configure the settings as per your requirements.
Then Go to Sale > Order > Info.You will see the Split Button on Order Info Page.