Add the CA signed certificates to the keystore

Good Morning,
I am currently evaluating ADSelfservice Plus and I have been following the instructions in the SSL Tool & Guide form within the GUI. So far I have found these to be excellent, I have reached the stage where I have to "Add the CA signed certificates to the keystore" and I can see that there are clear instructions for 3 major vendors; however I am wish to test with a certificate from "Let's Encrypt" for which none of the instructions appear to fit!

I now have 4 files: -
1. The original "SelfService.csr" file
2. 3 downloaded files from Let's encrypt
2.1 "ca_bundle.crt" file
2.2 "certificate.crt" file
2.3 "private.key" file

Any assistance of how to proceed with this would be appreciated.

Regards
Chris