can't get field.select("XXXXXX") to work

can't get field.select("XXXXXX") to work

I have a form <Contacts> with a field <Roles> (Lookup, Multi Select, Checkbox). In a script I want to select one of the values.

I use the following statement (after fetching the appropriate record in <Contacts> using Collection x):

x.Roles.select("Volunteer");

I get a message that this is not a valid statement.

What am I doing wrong?

thanks

Henk