views.py

def customer_list(request):
    current_user = request.user
    userP = UserProfile.objects.get_or_create(username=current_user)
    customer_list = Customer.objects.filter(company=userP[0].company.comp_name)
    # Assign
    form = AssignForm(request.POST or None)
    if request.POST:
        customer_id = request.POST.get('customer_id', None)
        customer = Customer.objects.get(id=customer_id)
        user = UserProfile.objects.get(id=request.POST.get('user', None))
        customer.user = user
        customer.save()
        form.save()
        return redirect('user:customer_list')
    context = {
        'customer_list': customer_list,
        'form': form

    }
    return render(request, 'customer_list.html', context)

customer_list.html

...
<button type="button" class="btn btn-success" data-toggle="collapse" data-target="#demo{{ forloop.counter }}">Assigned</button>
...
<form method="post">
     {% csrf_token %}
     {{ form|crispy }}
     <input type="hidden" name="customer_id" value="{{ customer.id }}">
     <button type="submit" class="btn btn-success ">Assign</button>
 </form>