When you open RIMMF, the software opens whatever is currently set as your default data folder of records, ready for you to work with those records.
Here are instructions on how to create a new data folder, without any records, and switch to using it.
See How to: Change to a Different Data Folder of RIMMF Records for how to change to an existing data folder, already containing records, and make it your default folder.
Every time you re-open RIMMF, the software will open this as your default data folder of records, until you How to: Change to a Different Data Folder of RIMMF Records.