Did I mess up my iMac Fusion Drive configuration with an Erase?

I got an iMac 2019 from my son and it has a 1TB Fusion Drive. He could not remember the password he set after clearing out his personal data and reinstalling macOS. So I thought to do an erase of the hard drive and starting over. I might have upon doing the erase with Disk Util messed up the Fusion Drive configuration (maybe erasing the wrong volume?). I did reinstall macOS but the performance was a real dog. I then saw online a suggestion to do a "diskutil resetFusion " in terminal during Recovery and then I reinstalled macOS again. Performance improved a bit but still quite bad (performance comparison is to my other Macs like a Mac mini). Can someone please explain how to run Disk Utility again from ground zero and set up the Fusion Drive correctly and then the reinstall of macOS procedure?