I have a file with Turabian Author-Date data which I would like to import. But if a choose import filter manager I can't select this format. How do I do this?
Because there is no such filter. You'll have to design one yourself -- the User Guide tells you how to go about this generally (it's often not perfect) -- see the section on importing an existing bibliography.
If you have an unnumbered bibliography to import, you can easily change it in your word
processor by doing a global Find and Replace, Finding Returns and Replacing them with,
for example,
return Ref:
(that is, [return character] [space] Ref: [space])