Setting s.visitorID using the Mobile SDK

We're trying to ensure the same visitor from web and a mobile app are counted as the same unique visitor, rather than two separate visitors.

According to this documentation: Connecting Users Across Devices

We need to set the s.visitorID for users that are logged in. This is easy to do in web via DTM, but how do we set the visitorID via the mobile app SDKs (iOS). (Note we currently don't have Experience Cloud setup - Analytics is the only Adobe product we're using, and as I understand it, regardless, we still need to set a custom visitorID