1. Replace the default managesieve plugin by sieverules
2. Copy the old ruleset to the place, where dovecot is looks for it.
In case of cyrus-imapd it’s here by default: /var/spool/sieve/
3. Rename it from ingo.script to ingo.sieve
4. Go to Roundcube -> Filters
There should appear a message:
Import filters: Another set of filters from Horde (INGO) has been found. Would you like to import these filters into your current set?