Hi Mahmoud,
The 2019a installation is probably corrupted. You can delete the installation folder directly. If you want to use the 2019a specifically then reinstall the product after deleting the corrupted installation. The default installation folder is as follows
Windows: C:\Program Files\MATLAB\<Release>
macOS: MATLAB_<Release>.app in Applications folder
Linux: /usr/local/MATLAB/<Release>
Hope this helps!