Update an existing pivot record

If you want to update an existing pivot record on the table, use updateExistingPivot instead of syncWithPivotValues.

 1// Migrations
 2Schema::create('role_user', function ($table) {
 3    $table->unsignedId('user_id');
 4    $table->unsignedId('role_id');
 5    $table->timestamp('assigned_at');
 6})
 7 
 8// first param for the record id
 9// second param for the pivot records
10$user->roles()->updateExistingPivot(
11    $id, ['assigned_at' => now()],
12);

Tip given by @sky_0xs