Do I have to close my existing positions before the restricted news event?

No, you don't have to be flat before the restricted news event. You can hold existing trades that are placed prior to the restricted news event but you are not allowed to close them or open new positions during the restricted period. Moreover, activated pending orders including SL at TP during the restricted period also serve as violations of the rule.

But if you wish to close them, you may do so before or after the restricted period.

NOTE: Trading restriction on selected news events only applies to FTMO Traders and on affected instruments.