Hello Elly,
As the other experts suggested, you can see a possible way of
1. Create variants with selection criteria in FBL5N. When the user call the variant, he may needs to change the dates criteria since this varies time to time. So the variant will be created by using the dynamic selection by giving the relevant customer numbers.
2. Use any field from Customer master - FBL5N which is common in both and fill the data in Customer master. When you call FBL5N, you can call that field and execute the report.
Thanks