Measure the wall angle at the corner
Set the miter saw to the correct spring angle
Set the bevel angle on the saw
Position the crown molding upside down and against the saw fence
Cut the left piece with the correct miter and bevel directions
Cut the right piece with the matching opposite miter and bevel directions
Test-fit the two pieces at the corner
Trim slightly if needed for a tight fit
Join the pieces with adhesive or finishing nails
Fill gaps with caulk or wood filler if necessary