If for some reasons required to change Justification of existing beam you need select beam and select option from menu Modify
Section
Justification.

You will see current Justification of selected beam.

Lets select form list TOS.

Click Apply.

Justification of beam is changed to TOS. You have to consider if you changing justifications of beam you will get this beam moved to new position. It can be not expected but you need to know it before creation of beam. Current position of middle beam is TOS.
Let