I change my password my wifi now my apple ipad won't connect to wifi

Start with basic WiFi troubleshooting - as detailed here:

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

Recommended settings for Wi-Fi routers and access points - Apple Support

WiFi/Internet connection difficulties are usually an indication that your device does not have a routable IP Address - your IP Address usually being assigned by DHCP. When problems occur, your iPad may only have a self-assigned link-local IP address that begins 169.254.x.x.

You can verify your DHCP-assigned IP Address from settings:

Settings > WiFi > [Your WiFi Network / SSID] - tap the blue “i” icon - [IPv4 Address] IP Address

If you have a VPN App or profiles installed, or a security App such as Norton, these may be interfering with DHCP and preventing your device from obtaining a valid IP Address for the WiFi network to which you are attempting to connect. The resolution is usually simple; if installed, you may only need to temporarily disable or remove the Security App and/or VPN.

DHCP is frequently used to automatically obtain an IP Address. Until your iPad has a valid IP Address to connect to your network, you will not have an internet connection. Disabling or removing VPN and/or the offending security App should allow DHCP to operate normally - allowing connection to your network and the internet.

If this resolves your issue, the VPN and/or security App can be reinstated after the connectivity problem has been resolved.

If some Apps are working as expected, while others are not - or other devices can connect to your WiFi network - you may find that a restart of your WiFi Router, followed by a restart of your iPad will clear the problem….

To restart your router, disconnect power from the router for at least 30 seconds - then reconnect power to restart. After your router reboots (which may take several minutes), force restart your iPad:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If you continue to have difficulties, check to see if your iPad is using the WiFi Private Address feature. This feature is intended to provide additional privacy and security when using “public” (untrusted) WiFi networks.

Settings > WiFi > [Your WiFi Network / SSID] - tap the “i” icon - Private Address

The Private Address feature is largely unnecessary for your home WiFi network; if enabled, Private Addressing can cause issues if specific MAC addresses are expected by your WiFi Router. You may need to disable this feature - and can be enabled or disabled for each individual network.

Use private Wi-Fi addresses in iOS 14, iPadOS 14, and watchOS 7 - Apple Support

When you rejoin a network under a new password, your iPad is assigned a new device IP address, but your iPad is trying to connect at the old assigned IP address - so it won't work.

The way around this is to go System Settings > Wi-Fi > Forget this Network and then choose the network from the list and join by entering the password again.

At least that is the way it works with my home address.

On a MacPro (my husband's) with Norton, the "Forget this Network" choice in System Settings is under Network, not WiFi. If you try to change the password in under the wifi name, it just glitches - looking like it is connecting and losing the connection and then can't even find the network if you try to enter the wifi settings manually. Even the Network choice in system settings might look blank - so you won't be able to manually change the DHCP.

If this happens, just restart and then go to System Settings > Network > network name i > Forget this Network. Then you will be able to join the network fresh. (Learned this painfully . . . . kind of like when you unplug the router/modem to reset it).