My old ipad unable connect wifi

Here is what might help: please go to the 2 links for information.

1: backup and then restore backup<https://support.apple.com/en-us/HT203977> <https://support.apple.com/en-us/HT204184>

Start here:

Connect to Wi-Fi on your iPhone, iPad or iPod touch – Apple Support

If your iPhone, iPad or iPod touch won’t connect to a Wi-Fi network – Apple Support

You may find that, counterintuitively, a restart of your WiFi Router will resolve a connectivity problem. To restart you home router, disconnect power - then wait at least 30 seconds before restarting. When you router has rebooted (which may take several minutes), force-restart your iPad:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.