At the moment, you can not enter long breaks - those lasting several measures - manually.
FORTE Premium features an option that enables multiple measure rests for. There need to be at least 4 measures of rest. Your score must consist of a single instrument OR you're working with a single part. You'll find that option in the main menu "Score" - "Layout" - "Options."
Click on "Options". A new window named "Edit Layout" opens.
Select the tab "Options".
In the middle of the window, you'll find "Enable multiple-measure rests".
Check the box.
Select "Apply" and "Okay"