Set MATLAB_ROOT environment variable

I have tried“MATLAB”) and I got the following error:

ERROR: Error building MATLAB:
ERROR: LoadError: MATLAB cannot be found. Set the “MATLAB_ROOT” environment variable to the MATLAB root directory and re-run“MATLAB”).

I am using Linux (Ubuntu 20.04.3) and the matlab directory is: /usr/local/MATLAB
I don’t know how to set “MATLAB_ROOT” environment variable?