[Rocky]

You'll have to completely purge clamav and it's definitions, then reinstall it.

Do something like:
apt-get remove --purge clamav* libclamav6
Delete everything from /var/lib/clamav if anything is there.

Do:
apt-get update
apt-get install clamav-daemon libclamav6

Make sure to configure clamav according to section 7 of the guide.

Let me know how you make out.