How to keep track of what is already currentstep ==2 and perform a second check?

Question

Vue.js

There is a form with 3 steps.
I add a check for dustiness of the field and deactivation of the button and the Disabled button if the required field is not filled.
watch is executed only at the first step.. does not react further..
how to modify ?

watch: {
      formData: function(step) {
        if (this.where_buy == null && this.currentstep === 1) {
          this.isButtonDisabled =false;
        }
      }
    }