Read Numbers 10:6 Using Other Translations
When ye blow an alarm the second time, then the camps that lie on the south side shall take their journey: they shall blow an alarm for their journeys.
And when you blow an alarm the second time, the camps that are on the south side shall set out. An alarm is to be blown whenever they are to set out.
When you sound the signal a second time, the tribes camped on the south will follow. You must sound short blasts as the signal for moving on.