Based on your screen snapshot provided, it appears that one of your source data is ECC. For the ECC data, create an info set on top of the ECC table and create your universe in BI4 ( supported SP3 and greater only). For the excel flat file data source request your ABAP team to setup a custom program to load the data into ECC Z table (aka custom table in ECC). Then you can join both the tables within info set in ECC or use a single universe connection and join the ECC table and ECC- Z table.
Hope this helps. Good luck!
Rama