Vuejs 2 state variable problem

I am new to vuejs and I am trying to pass a state variable to a local component variable so to manipulate just the local variable.
I have the error bellow ,how can I solve it?

Error: [vuex] do not mutate vuex store state outside mutation handlers.

My code is bellow.

mounted() {
this.toDelete=this.pconflict;

}
,

computed: {
pconflict(){
return this.$store.state.productModule.conflictContainer
}
,…
}
methods: {

goToSaveConflictTable() {

this.toDelete.merge_container[0].product_conflict.product_domains[0].domain_urls.splice(1, 1);
}

}