Assuming you have it connect to your TV directly with an optical cable, and you have the DVD connected to the TV with HDMI you may need to use the TV menu to turn on the output for the input you have the DVD connected to.
The soundbar seems to have HDMI inputs so you could also connect the DVD to it with HDMI and it to the TV with HDMI. If you use a set to box then connect it to the soundbars are well and use that to switch.