Change resolution on iPadOS 18.3 (22D63)

All models of iPad have a fixed screen resolution determined by their screen.

What can be configured is the iPad Display Zoom setting.

Settings > Display & Brightness > Display Zoom - select as required from available settings

When connected to an external monitor, the display resolution is determined by the EDID data provided by the connected monitor.

Why?

iPads have a fixed resolution and in general changing it should not be necessary.

Why exactly do you need this?

Perhaps there's a different solution to your issue that does not involve changing resolutions which cannot be done.