Extract the zip-Archive - downloaded from the Release-Page - open the plgx folder and copy the KPSimpleBackup.plgx file into the Plugins folder of your KeePass installation. This also works with the portable version of KeePass.

Extract the zip-Archive - downloaded from the Release-Page - open the dll folder and copy both, the KPSimpleBackup.dll and the Ookii.Dialogs.WinForms.dll file into the Plugins folder of your KeePass installation. This also works with the portable version of KeePass.

ℹ️ It is also possible to copy all three files into the Plugins folder and KeePass will decide by itself which of them it should use.