It is because it says that I have to have MacOS 10.15 or later. & I have MacOS 10.14.6. & How can I fix this problem on my MacBook Air?

Scottyhino315 You'll need to update your OS to Catalina (10.15) or newer. That's simple enough: any Mac that can run Mojave (10.14) can also run Catalina. Search the App Store for the OS you want to install. Please keep in mind that Mojave is the last version of macOS to support 32-bit apps. So if you upgrade to Catalina or newer, any 32-bit apps you're currently using will stop working.

Scottyhino315 Search for the version of macOS you want to install. Or alternately, use these links: https://support.apple.com/en-us/102662

Ok.🆕 and What do I search for in the App Store?