[Vuejs]-How to change the default message of the required field in the popover of form-control in bootstrap-vue?

But answer as follows.

To disable popover messages

<b-form-input id="email" v-model="form.email" type="email" :state="null" 
         placeholder="Enter email"></b-form-input>

To add custom messages, you should change a property :state as true or false and add label to make sure what is error.