First make sure you installed the Bridge Designer software, rather than running it directly from the downloaded disk image. To do this, follow the instructions in the Readme file that comes with the image: In the Finder that appears after mounting the downloaded image, drag the Bridge Designer icon into the Applications folder.
If you had already correctly installed the Bridge Designer and wish to re-install it to correct a problem, follow these 3 steps:
(1) Start a Terminal (usually this is found in Utilities) and give the following command (which you can copy and paste into the terminal window):
rm -rf ~/Library/Application\ Support/WPBD2016
Type <enter> at the end to execute the command.
(2) Open your Application folder and drag the Bridge Designer 2016 into Trash.
(3) Mount the downloaded disk image again (by clicking it in Finder) and in the Finder window that pops up, drag the Bridge Designer 2016 icon to Applications.