Please find the course details by St John as follows
http://www.stjohn.org.hk/b5/timetable.shtml
From the website above, you can find a course held in Yuen Long
You can also refer to the Hong Kong Red Cross's website as follows
http://www.redcross.org.hk/home.cfm?Mid=1531&FMid=113&SMid=116&popup=0&langid=2&Ver=G
No courses orgainsed by Red Cross are found