basically you just have to sign and publish an empty kind 3 event. Normally it stores your follows in the tags. If you publish one with no follows, boom, fresh empty list. See NIP-02

NIPs

NIP 2 - Follow List — Nostr Implementation Possibilities

A special event with kind 3, meaning "follow list" is defined as having a list of p tags, one for each of the followed/known profiles one is follow...