Alt + Left Mouse Button to pan
Middle Mouse Button to pan
Mouse Wheel to zoom in or out
Left-click to select a Tile
Left-click drag to select multiple Tiles
Select the desired palette from the drop-down menu. Click on the Edit button at the side of the palette selection menu.
Adjust the Palette using the Tile Palette tools just like editing a Tilemap in the scene. When done, click on the edit button to exit editing mode. Remember to save your project to save the Palette!