First, you need to setup the communications template in dash manager.
This obviously involves setting the base address, the offset, length and bitmask for the messages that you are after.
Once you have done this, you need to add the newly created channels into the display list to transmit the message over onto display creator.
After this is complete, and you save the dash manager file, the application should also automatically save you a .DBC file along with the dash file, this file is used within display creator to generate a channel list, and then allow you to use the channels in the display you are setting up.
There are a few examples of this within display creator itself. If you create a new display creator file and scroll down within the template window, there is a template that has indicator icons, highbeam icons etc etc. If you have a look at how these work, you should be able to setup your own version of this using a switch for the flashing functionality.
You may like to have a look at the following links to get you started:
https://www.motec.com.au/webinars/webinararchive/#DChttps://www.motec.com.au/filedownload.php/display_creator_user_manual.pdf?docid=4628