Follow steps below to easily obtain the CSR file :
Step 1 : Open Utilities on your Mac
Step 2 : Open Keychain Access
Step 3 : Click on Keychain Access
Step 4 : Click on Certificate Assistant
Step 5 : Select Request a Certificate from a Certificate Authority from the menu
Step 6 : Select User Email Address and provide CA Email Address
Step 7 : Select Saved to Disk and click on Continue
Step 8 : Click on Save
Step 9 : Click on Show in Finder
Step 10 : Here is your CSR file