Turn off: I believe in the user map is the possibility to set font = 0 (Major/Minor contours). This could be turning off the depth values. If not, use the shape export, open the attribute table in qGIS (in this case Excel also possible) and set the MODE values to "N" or delete all numbers in the column VALUE.
Turning the depth values is not a RM function. It is IMC preset. If You want to turn the values, use other GIS applications. This will be give a Picture with turned values, but not a chart for Lowrance units with turned values.
Best wishes
fjordfisher