Yeah, first create domains and mailboxes.
Then you can find user's Maildirs here for example:
/var/lib/docker/volumes/mailcowdockerized_vmail-vol-1/_data/DOMAIN/USERNAME/Maildir
If you done with the restore, remember to execute:
docker exec mailcowdockerized_dovecot-mailcow_1 chown -R vmail:vmail /var/vmail
docker exec mailcowdockerized_dovecot-mailcow_1 /usr/bin/doveadm quota recalc -A