This is a good question. Fortunately, there is a video and you can find a link to directions at this link.
I suggest watching the video carefully in order to make a self determination on whether this is a repair you can handle on your own or not.
If it is, then you can simply purchase the hose and handle assembly and make the repair.
If you have an older hydrofloss or if you think you cannot make the repair, you might consider purchasing a new HydroFloss here.
Note that the hose and the handle come as one piece and they are not separable. If you have a leaky hose, then you must replace both the hose and the handle as one piece. (again, please watch the video on the above link).
Here is a picture of what the hose and handle assembly looks like: