If you used any other password managers, you need to make sure that the .CSV file you have is matching our import criteria. Use the picture for some guidance:
It's important to organize your data based on headlines. Please note that the first line of the categories need to be exactly the same as shown in the picture with lowercase letters. Sometimes you will need to add extra categories like note or type, if there are none, and you are ready for import.
To import your passwords, go to Settings → Import/Export → Other if others are not relevant. Then select the CSV file you want to import and click Open and then confirm by clicking on Import Selected.