Jump to Mobile
When making a selection, sometimes you don’t grab everything the first time. When this happens, instead of re-selecting everything, use 
Add.
Adding to a selection in Sketchbook Pro for desktop
Once you’ve made a selection, tap 
, then either tap-drag to add to your selection or for Magic Wand selection, tap other areas.
NOTE: If Magic Wand was selected, increase the Tolerance to add pixels to your selection, then tap the canvas again to see the change.
Adding to a selection in Sketchbook for mobile devices
- Once you've made a selection, tap
and then 
. Then either tap-drag to add to your selection or for Magic Wand selection, tap other areas. - Tap
to accept the changes or X to decline.