How can I keep selected the previous value when updating a form?

I am using laravel collctive form. I want to update only the quantity field of the following form keeping the blood_id field readonly. When I submit the form I am not getting blood_id value.

How can i solve it?

{!! Form::model($bloodBank, ['route' => ['bloodBanks.update', $bloodBank->id], 'method' => 'put']) !!}
    <div class="row">

        <div class="col-lg-8">
            <div class="form-group">
                {!! Form::label('blood_id', 'Blood Group', ['class' => 'form-control-label']);!!}
                {!! Form::select('blood_id', $bloods ,  null , ['placeholder' => 'Choose Blood Group',"class"=>"form-control",'disabled' => true]) !!}
             </div>
        </div>

    </div>
    <div class="row">

        <div class="col-lg-8">
            <div class="form-group">

              {!! Form::label('quantity','Quantity', ['class' => 'form-control-label']);!!}
              {!! Form::number("quantity",null, ["class"=>"form-control form-control-label",'min'=>'0']) !!}
              <span class="validation-error">{{ $errors->first("quantity") }}</span>
              
            </div>
        </div><!-- col-12 -->

    </div>
    
    <button class="btn btn-info">Update </button>
{!! Form::close() !!}