Accessing Multiselect Field from another Form?

I have a user information record (setup by Form A) that has a multiselect field (Fielda) that is set by doing a lookup to another form (Form B)

Now i need to access my user information from Form C to verify correct access.

So, i can easily access the Form A information that is "native" to Form A - but how do i access the multi-select field in Form A that was set by the lookup field from Form B. (they were string fields originally setup in Form B)

hope that makes sense

thanks