It can be done via the following API call.
The account that is removing the user will need the following permission.
To enable to API and generate an API token follow the instructions on this article.
Another option is to disable SAML for a while, delete the local users and enable it back.
**Please note that, if the user is removed from the idp provider (AD, Azure AD, OKTA...), it needs to be manually removed from IriusRisk as well.