”Using the occ command” documents using versions:cleanup either globally or for specific users, with example invocations for both cases. However, said examples are identical in the current revision:

This example deletes all versions for all users:

sudo -u www-data php occ versions:cleanup
Delete all versions
Delete versions for users on backend Database

[…]

You can delete versions for specific users in a space-delimited list:

sudo -u www-data php occ versions:cleanup
Delete versions of   freda
Delete versions of   molly

Unless I’m misinterpreting this, the latter example should have the space-delimited list of users following the invocation, like so:

sudo -u www-data php occ versions:cleanup freda molly