We don’t have the direct support of general CSV file import at the moment. Honestly, we don’t support import from flat files at all. We only support import from Easy pass export and from browsers (Chrome and Firefox)
We are considering proprietary format, but it is not yet implemented. If you can convert CSV to the chrome or firefox will import we can grab it from there and we delete it from browsers afterward.

How to import data for chrome/firefox is shown here, but for your case, you would need to convert your CSV to format chrome/firefox will accept.
https://www.avast.com/faq.php?article=AVKB273
https://www.avast.com/cs-cz/faq.php?article=AVKB274

Once you have data in your browser they will be imported either during avast passwords setup or later from Settings->Passwords using import button.