How can I extend the AppleCare Plus for my Apple Watch Series 3?

My Apple Care Plus coverage plan for my Apple Watch Series 3 is ending very soon & I cant find any-where on the Apple site to extend it monthly (monthly plan). When I bought it I paid up-front for the 2 years coverage plan & I know I can extend it monthly ... I just can't for the life of me find where I can do this.

Can anyone please help!