1. First we need to download a program called Advanced RAR Password Recovery. It's not free cost $30.00 but I have a secret key. You can download it for free from here.
2. During the setup you will be asked to enter a key enter this key (for the full version)
3. Click the folder Icon under Encrypted RAR file and search for your RAR folder you need the password to.
4. Select all options under "Brute-force range options".
5. Click Start at the top and let it do the work for you. This might take hours depending on password length.