turn with accidentals.

Here's something from the manual:
"Add accidental to an ornament
To apply an accidental to an existing ornament, such as a trill:

Select the note to which the ornament is attached;
Open the Symbols section of the Master palette;
Search for and apply the desired accidental to the score (small accidentals can be found using the search term "figured bass");
Drag the accidental into position (or reposition using keyboard shortcuts or the Inspector)."

Or instead of search, Add/Text/Figured bass then type b or #.