With the installation of "GAEB-Online 2021" a sample file is installed on your computer. You can use this file to test the import, or you can use this file as a template for your Excel data.
You can find this sample file via Start | Program group "GAEB-Online 2021" there the folder Import Sample or as a link with the name "GAEB-Online - Link to Import Sample" on your desktop.
The setup will install the pattern files for the user into the folder "C:\Users\<Username>\AppData\Roaming\"GAEB-Online 2021"\Pattern_Import", where <Username> is then the username you use on this computer.
If you can't find the sample file for import, you can also download it directly from here https://www.gaeb-online.de/download/Import_Muster.xlsx.