In order to use the renewed certificate, you need to have taken a backup of the existing keystore file (created while configuring the SSL), which was taken before the installation of any certs. If this file is present, then you can replace this file in the [ServiceDesk Plus - MSP Home]\jre\bin folder and follow the instructions from Step 3: Install your SSL Certificate.
If you do not have a backup of the keystore file, then you need to start from scratch i.e., from Step 1, and get the certificates reissued for the new CSR (Certificate Signing Request).
You can use the following command to get the list of certificates installed in the keystore.
Keytool.exe –list –keystore sdp.keystore
Below is an example of how a keystore looks before installing any Certificates. It will only have the keyEntry.