To upload the cloudfront private key to the instance, kindly follow the below steps:
1. Open WinSCP in windows.
2. Enter the instance public IP in the Hostname section.
3. In the "Advanced" drop-down, select SSH, then in Authentication section, choose your private key that you used for launching the instance and select OK.
4. In the Username section, enter "bitnami".
5. Click "Login".
This will let you access the instance & you can put your private key in the instance.