How to override the widget of a field in the administration of Django

admin.py

class IssueAdminForm(forms.ModelForm):
    class Meta:
        model = app_models.Issue
        fields = ['title', 'labels']
        widgets = {
            'labels': app_forms.ArrayFieldSelectMultiple(
                choices=app_models.Issue.LABEL_CHOICES),
        }

class IssueAdmin(admin.ModelAdmin):
    form = IssueAdminForm