You can not rollback MATLAB updates after they have been installed.
In order to revert to a previous update, you will need to uninstall the current MATLAB version, then reinstall with the offline installation files. To retrieve the update-free offline installation files of MATLAB, download the ISO or run the installer to download MATLAB using the 'download only' option.
Please note that for R2019b, you can obtain an ISO with updates already applied.
For more information on obtaining the offline installation files for MATLAB and the desired MATLAB update, please refer to the following articles:
How can I get MATLAB installation files for use on an offline machine?
How can I download and install a MATLAB Update manually?
NOTE: You will need to be a License Administrator to obtain the offline installation files.