How to push values to property array in Cypher?

Adding values to an array is analogous to incrementing an integer or concatenating a string and is signified the same way, in your case (let c be your [c:contains {id:[12345]}])

c.id = c.id + 1111             //  [12345,1111]
c.id = c.id + 14567            //  [12345,1111,14567]

or

c.id = c.id + [1111,14567]     //  [12345,1111,14567]