Log into Keeper's web vault at https://keepersecurity.com/vault/
Click on your account email in the upper right-hand corner.
Click on Settings > Import.
If the .csv file was from a specific application, choose the company it was exported from. The default "Text file (.csv)" will be used if a company is not selected.
Drag the exported file into the target window "Drop a File Here"
Use the drop-down menu in each column to map to a Keeper field.
Click on Import.