Click on the Search Icon at the top right of the screen and search for Keychain Access.
In Keychain access, select System in the left-hand menu.
Select “Keychain access > File > Import Items…”in the top menu
You will find the certificate in the download folder. You will be asked for your Mac Book password, put this in to import the certificate.
Once imported, double click it to open. Next to Trust, click the arrow > and select Always Trust .
Go to Settings > General > About > Certificate Trust Settings
Turn on the SonicWall certificate you have just installed.