Without knowing the model number of your 5.1 speakers we don't know what connection options you have or which one you used.
If you use HDMI ARC you would have to have ARC in both the TV and 5.1, have connected the 5.1 to the ARC marked HDMI input, turned ARC on in the TV and selected it as you source in the 5.1
If you used an optical cable then go into the TV audio set up menu and select a different audio type then the one it is set at now.