How to turn valve off

[MT1979]

Our fridge freezer has an external water filter, we had builders in and they knocked the filter and it is now leaking.

There is a valve connecting the filter to the water supply, however I can’t work out how to turn the water off. There is a small threaded hole on the front about 5mm wide, is there something I need to insert in there to turn it?

 

[ShaunCorbs]

Any pictures should be a washing machine valve eg brass nub with two flats if so need to use some pliers to turn the flats 90 Deg