Go to Beam Settings - End Cuts and Reference Axis Panel, or the Start/End angle controls in Beam Info Box.
Define the Start and End edges of the Beam as angle as horizontal, vertical or custom.
Note: Horizontal available for slanted Beam only.
You can also edit this geometry graphically:
–Select a Beam in 3D. Click on its end surface, then choose Rotate Join Angle from the pet palette.