You will not be able to allocate a specific userToken to a specific variant - this is done at random by the AB Test.
Users are identified by setting a userToken and if you’re using InstantSearch or the API clients - you can set the userToken in the headers or search parameters.
You can review the following documentation regarding how our AB test allocates users to different variants (A or B) https://www.algolia.com/doc/guides/ab-testing/ab-test-implementation-checklist/#identify-your-users to understand how it works.