SM-G925W8 Repair IMEI Help with Steps

I am trying to repair IMEI of a SM-G925W8.

1. I have rooted phone using CF Autoroot

Because i don’t want to brick the phone, I want to make absolutely sure I have the steps correct.
I have backed up the EFS & Cert

Do I simply enter the IMEI I want to change to and hit repair?

Or do I need a "cert" file that is clean or un blacklisted or whatever?

Or as one youtube video shows I

1. load in modem file
2. repair imei
3. patch certificate

I know this may have been answered before, but I have been searching
for a few hours and there are no definitive steps?

Can cert files be created?

I know this may seem like child’s play to some of you, but I have been entrusted with a customer’s phone that is quite expensive, so you can see my trepidation in proceeding without a clear understanding of this process.

Thanks in advance for patience and willingness to help.

(I searched, honest!)