Hi, my HomePod has not worked in weeks now trying to fix it. Can't even find the app in the app store

You need the Home App installed on your iOS device so you can Reset it, then set it up again

Reset HomePod - Apple Support

Set up and use HomePod - Apple Support

• Update the software on your iOS device before proceeding with Set up.
• Then update your HomePod after you’ve set it up
• It should be in your App Store. Search “Home”. If it says “Open” like my screenshot, you have it and it’s perhaps hidden in a folder on your screen. Or you might also see it in your Control Center.. Otherwise install the App

Try Restart HomePod from the Home App: 

Open the Home App - go to the Room it’s in 

Long press on the HomePod icon to bring up settings, scroll down to the gear icon, tap that, scroll to the bottom to Reset HomePod - then select Restart HomePod 

• Reboot wifi also

If you got a new iPhone, reset HomePod then set up with your new one and it’s easier to solve your problems if you telll us what is “not working”

There is no HomePod app. This is the home app for HomeKit. This is what you need to set up and view settings for the HomePod