To unhide a preset tap on an image and tap on the edit icon, .
Hold down on a preset till the presets start to animate.
When the presets are animated you can tap a preset to hide it from your dock. When a preset is hidden it is greyed out from dock as shown here:
If you wish to unhide a preset, tap on the grey out preset to unhide it from your dock.
This process is also the same for tools.
When you have completed organizing your presets and tools. Tap anywhere on the screen to save your preferences.