Use a previously emitted SSL certificate for same website but new IP adress

Hi, I got a installed on my Forge website a SSL certificate from my registrar to which I provided Forge CSR. After re-creation on my server and redeployment, my website sites at another IP adress but with same name.

How i can use the previous SSL certificate, knowing SSL certificate are name based and not IP based? I dont want to regenerate a new SSL certificate with a new CSR from Forge but to keep the same previous one. Forge has an install existing certificate options, but it asks a private Key?? with the certificate.

What is the Key that Forge use when generating a CSR?(private key are used to generate the CSR, and checked against the approved certificate).