The Dash should fit tightly in the mount, so if you are experiencing lots of wobbling of the Dash, we should first make sure you are removing the Dash using the thumb tab. Here are 2 videos to help show the correct and incorrect way to use the mount:

Of course, this does not help you now that the Dash is loose. First thing to try is to use the provided, or any, T6 Torx screwdriver to tighten the 2 bolts on the underside of the mount. If this does not help, contact support@stagescycling.com for more options.