Django MultipleChoiceField field with filter

Question

what should I write here to filter participants by event ID forms.py

participants = forms.ModelChoiceField(queryset=Participant.objects.none(), empty_label=None,),

so that I do not write to the queryset, I get all participants from all events. And I need to see those participants who sent an application for this event

view.py

form = EventForm(request.POST or None, instance=event)
form.fields['participants'].queryset = Participant.objects.filter(event_id=Event.pk)

would be very grateful for help