Step 1 – Login to your Exchange 2007 server
Step 2 – Click on the 'Start' menu and go to 'Programs'
Step 3 – Go to 'Exchange Management Shell' from the 'Microsoft Exchange Server 2007' in the programs.
Step 4 – From this page, copy and paste the NewExchangeCertificate command onto the window of 'Exchange Management Shell' and press 'Enter'
Step 5 – You can now find the new CSR file, with '.exe' extension in the root of your C: drive. It would be named as per the path option in the command itself.