Hi, Marian! To me, strumming is the most important aspect of dulcimer play. Thus, it takes time to settle-in to learning how to strum and feel comfortable strumming. (I'm always working on my strum and I've been playing about 6 years.)
I suggest this exercise: Put on any music you enjoy. With your left hand, mute the strings. With your right hand, experiment strumming rhythms with the music. It really helps one get a feel for rhythm and, over time, your strumming will improve.
Happy strummin'!
updated by @robin-thompson: 02/16/16 08:52:47PM