You're basically manually adding the certificate to the root certificate store manually. That file is /system/etc/security/cacerts.bks on your phone, so you need to start by getting that file from your phone to your computer. Adb is not the only way to do that. If you have it set up, just type in the command it says to run. If not, there are many other ways to do it. Any form of a terminal emulator will help you copy it out, or you could just use root explorer.