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It is possible that the Excel app is corrupted. We may need to delete it and redownload it from App Store. So first, I want you to backup all your excel files to your computer or OneDrive
Then reset your iPad and see if it works or not. Press and hold down the Power button and Home button at the same time until it shows the Apple logo. When you see the Apple logo, release the buttons and let it boot. Print from Excel.
If that didn't work, then go to Settings > General > Reset and tap Reset All Settings. Remember this will reset some settings like bluetooth, WiFi, wallpaper etc. So you will have to reconnect to your WiFi after resetting all settings.
Then open Excel and try to print.
Please let me know if that didn't work, so we can continue troubleshooting.