iOS/iPadOS doesn't offer the ability to set an order of preference for WiFi networks. Your iPad will automatically reconnect to the last used WiFi network; if not available, of configured WiFi networks for which Auto-Join is enabled, the iPad will connect to the WiFi network that has the best signal.
As mentioned by Carol B., the best that you can achieve is to individually disable the Auto-Join setting for each WiFi network that you prefer to not use with your iPad - or delete unwanted WiFi network connections entirely.
Apple does invite submission of comments and feature requests via its Product Feedback portal. If you would like to see additional functionality or controls introduced in a future version, this would be the most appropriate channel though which to communicate your request to Apple:
Feedback - iPad - Apple