Update nodes property without duplications

Hi

I have a node with some properties, and i would like to update it to add a new value to one of the existing properties using merge, which is probably the incorrect solution

If i do a search, i can see that the new value is there but.. instead of updating the existing node, it has created a new one.

What is the right way to update an existing property in a node without duplicating it?

Thanks

fixed it with set :)