I understand that you are unable to install the app for the HP Officejet 8720 printer.
Please try the below steps and check.
Install the HP Smart app and set up the printer
Install the HP Smart app on a mobile device running Android OS 7.0 (Nougat) or later, Apple iOS 11 or later, or iPadOS.
Go to 123.hp.com from a browser on your phone or tablet and install the HP Smart app.
Make sure your mobile device is connected to your wireless network, and then open the HP Smart app.
iOS 13 and iPadOS: Allow Bluetooth and location permissions, if prompted.
For more information about how the HP Smart app uses Bluetooth and location, go to Why does the HP Smart app need Bluetooth and location permission in Frequently asked questions (FAQs).
Add your printer to the app.
Restrictions in Android 7.0 (Nougat) and later might prevent Wi-Fi printer setup using the HP Smart app for Android. If the wireless printer setup is not successful, go to 123.hp.com from a Windows or Mac computer or an iOS or iPadOS device to set up the wireless connection using the guided HP installation. You can also connect the printer with the wireless setup wizard on the control panel or use Wi-Fi Protected Setup (WPS). Once connected to Wi-Fi, HP Smart can discover the printer to enable printing. Go to Printer Setup Fails with HP Smart App (Android) for detailed steps.
If your printer displays, continue to the next step.
If your printer displays with Set Up, tap the printer, follow the on-screen prompts to finish setting up your printer, and then continue to the next step.
If your printer does not display, tap the Plus sign to select a printer from the list of found printers or set up a new one, and then follow the on-screen instructions.
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