Standard PS3 consoles cannot simply "go back" to an older version. Attempting to install 4.88 over 4.89 OFW via USB will usually result in a "Data Corrupted" error.
If your goal is to install CFW, you do not need to downgrade to 4.88. You can install CFW directly on 4.89 using a hardware flasher. Downgrading to 4.88 is only necessary if you prefer a specific CFW version or need compatibility with older tools.
Install Rebug Toolbox or use the “Toggle QA” pkg. If you don’t know what this is, assume you don’t have it.