Extend AppleCare–Plus coverage on my 2018 MacBook Pro?

I'm hoping to extend the AppleCare Plus coverage on my 2018 MacBook Pro. Can't get to any page that gives me options(s) to do so, nor tells me I cannot. I'm repeatedly cycled back to support.apple.com . Anyone know the proper URL––or the answer (as to whether an extension is even possible)?

I purchased this laptop at a Virginia Apple Store and paid at that time for AppleCare+ . That original coverage will expire January 22, 2022.

I was recently in a different Apple Store location and was told that store personnel could not effect an extension, but strongly suggested I call AppleCare directly to ask if I could purchase further coverage one I run out in January. The nice guy I spoke with at AppleCare Support took me to support.apple.com , and though we were able to view my currently active AppleCare+ account (and my Mac's identifying) details, neither of us was able to go to any next step.