Please follow the process given below:

​Import the Certificate

In order to import the certificate, you need to access it from the Microsoft Management Console (MMC).

1. Open the MMC (Start > Run > MMC).
2. Go to File > Add / Remove Snap-In
3. Double Click Certificates
4. Select Computer Account.
5. Select Local Computer > Finish
6. Click OK to exit the Snap-In window.
7. Click [+] next to Certificates > Personal > Certificates
8. Right-click on Certificates and select All Tasks > Import
9. Click Next
10. Click Browse
11. Select the .cer, .crt, or .pfx you would like to import. Click Open.
12. Click Next
13. Select Automatically select the certificate store based on the type of certificate.
14. Click Finish & OK

The certificate is now visible in IIS.

Export the Certificate as a .pfx

1. Open the MMC (Start > Run > MMC).
2. Go to File > Add / Remove Snap-In
3. Double Click Certificates
4. Select Computer Account.
5. Select Local Computer > Finish
6. Click OK to exit the Snap-In window.
7. Click [+] next to Certificates > Personal > Certificates
8. Locate and select the certificate for the correct domain.
   Right Click and select All tasks > Export.
9. Press Next
10. Select Yes, export the private key.
11. Choose Personal Information Exchange - PKCS#12 (.PFX) for the certificate file format. Check the boxes for: 
    Include all certificates in the certificate path if possible
    Export all extended properties
    Click Next.
12. Enter a password for your private key. Press Next.
13. Click browse and save your .pfx
14. Press Next > Finish > OK.