[Vuejs]-How to set the computed value on a property of an object in Vuejs?

If you want to use a dropdown to select it, try v-model: https://jsfiddle.net/wostex/63t082p2/1/

If you want to change data property by some event (i.e. click a button), then use a method. Call this method like this @click="methodName"

If you describe your task in detail, I can suggest a solution.

If you absolutely need to use a computed property for some reason, you should read this: https://v2.vuejs.org/v2/guide/computed.html#Computed-Setter

Anyway, name of your computed property should be different, than a data property.