Extract the zip file.open the 2.3x/2.x folder.Upload admin,catalog folder to your server from the "Upload" folder.
Upload the install.ocmod.xml file from Extension Installer.
Refresh the Modifications from Extensions > Modifications.
Please grant the permission to the user groups.
Then Go to Extensions > Modules.You will see the Deal of the Day module.Click on Intall.
Enable the Deal of the day Discount.
After successful install You can configure the settings as per your requirements.