Laravel 5 Keep old input for bootstrap multiple select in edit form and get it values in controller

In Laravel 5.4, I have an edit form with multiple select option as below code:

Problem: After the form is submitted, all options (bot from database and manually selected) are deselect.

Form validation:

$validator = Validator::make($request->all(), [
   'id'            => 'required',
   "location.*"    => 'required|string|distinct|min:1',
]);

Question 1: How can I keep the old input of this multiple select option in the edit form work?

Question 2: How can I store the form value as array into the database?

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