Python: Model.objects.all() - how to iterate through it using POST checkboxes

I have been building a CSV export using Python/Django. While sending all items listed in the change list everything works like a charm.

Now, I've been trying to use Action dropdown and export only those items selected via the checkboxes, but I cannot make it work.

My current code, the one that works even with the Action dropdown yet exporting ALL items, regardless of what was checked:

def export_this_list(self, request, queryset):
    """Generates participants list in Excel sheet."""

    csv_elements = Enrolment.objects.all().order_by('-training__date')
    for elem in csv_elements:

When csv_elements is swapped with request.POST.getlist obviously nothing works.

def export_this_list(self, request, queryset):
    """Generates participants list in Excel sheet."""

    csv_elements = request.POST.getlist('_selected_action')

or

    csv_elements = []
    for o in request.POST.getlist('_selected_action'):

Question: what is the syntax to combine my Model with the POST action?