Issues with MacBook Air Battery Health and AppleCare+ Coverage

I have AppleCare+ for my MacBook Air, and it's nearing its expiration. About a year ago, my battery health was showing around 86%. Over time, the percentage unexpectedly increased to 92%, which was both surprising and encouraging. However, despite this improvement in the displayed percentage, the actual battery performance was significantly worse than when it was at 92%. Now, a few months later, the battery health display has dropped back to 86%, but apps like CoconutBattery and AlDente show it at just 79%. My battery life is poor, and I'm concerned that I won't be able to get it replaced through AppleCare+ before the coverage expires. What do I do ?