Press on the Layers Button in the Top Toolbar.
Tap on the desired layer for merging in the Layers Menuand press on the Merge Down Button. In this example, Layer 2 is chosen as indicated by the dark gray highlighting.
The selected layer is merged with the layer below it in the list. Two layers now reside within the Drawing Canvas since Layer 2 and Layer 1 have been merged into one layer.
Note The Merge Down menu choice is only enabled when a layer resides below the selected one.