It happened at premises in the Rathgael Road area of Bangor on Sunday, August 26.
Shortly before 9.25 pm police received a report that a man entered the premises and produced a knife and demanded a member of staff to open the till, they were unable to do this.
The suspect made off empty handed.
The member of staff was not injured during this incident, however she was left very badly shaken.
Detective Constable Paul Downie would appeal to anyone who witnessed any suspicious activity in the area or anyone who has information about this incident to contact detectives at Bangor on the non-emergency number 101, quoting reference 1279 26/08/18.
Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111, which is 100% anonymous and gives people the power to speak up and stop crime.