If I understand you correctly, the csv file is data that you want to import into a Memento library.
There are a number of requirements that the csv file must meet:
1. The first line of the csv must be the names of the fields.
2. The field names in the csv file must match the Memento field names exactly .
3. The order of the names must also exactly match the order in Memento.
To locate the Memento directory go to the Memento main menu, select Settings > Database location.
The popup will show two locations. The one that ends in memento.db is the one you want.
However the easiest way to do it is to upload the file from your computer to Google Drive, right click on it, and open it with Docs. This will create a spreadsheet that you can link to.
From the open library; Link to Google Docs > Link to existing document and select the correct one.
That should import the data into your empty library. NB If the library isn't empty the existing data will be overwritten.