On a Mac connected to the same network as your Home Pod open the Home app, then right-click on the Home Pod and select Accessory Settings. Scroll down to see what version of podOS it is on. The latest is 17.5
On an iPhone open the Home app, then tap and hold the Home Pod button. When the Accessory Settings pops up tap it and scroll down to see the version. You can also initiate a an update with the Home App on an iPhone.
You could also first try simply restarting your HomePod or removing power from it for a few minutes and then plug it back in.
And of course, make sure your Apple Music account is paid up if you have a subscription.
Restart HomePod - Apple Support
If you are using a Windows PC then take a look here
Use HomePod with iTunes on PC - Apple Support