What’s the command you’ve been trying to run? You might try the built-in non-GUI test run first to see if the core binary works:
If that does not fly, you’ll probably need to compile the binary from scratch. It’s easy to do, see instructions at schorschinho/LCModel: A collection of compiled LCModel binaries for various operating systems. (github.com) and also in this thread. There’s test data in the repository, too.
PS: If you’re new to the MRS world, getting started on LCModel can be a daunting task. The GUI is very clunky to use and is really only a point-and-click tool for designing the control file, which is much more efficiently created by writing some code. What’s the kind of data that you are looking to analyze?