src/Checkout/Component/AddressBook.php
public function getExistingAddressFields()
    {
        $member = Security::getCurrentUser();
        if ($member && $member->AddressBook()->exists()) {
            $addressoptions = $member->AddressBook()->sort('Created', 'DESC')->map('ID', 'toString')->toArray();
            $addressoptions['newaddress'] = _t('SilverShop\Model\Address.CreateNewAddress', 'Create new address');
            $fieldtype = count($addressoptions) > 3 ? DropdownField::class : OptionsetField::class;

            $label = _t("SilverShop\Model\Address.Existing{$this->addresstype}Address", "Existing {$this->addresstype} Address");

            return FieldList::create(
                $fieldtype::create(
                    $this->addresstype . 'AddressID',
                    $label,
                    $addressoptions,
                    $member->{'Default' . $this->addresstype . 'AddressID'}
                )->addExtraClass('existingValues')
            );
        }

        return null;
    }
public function getExistingAddressFields()
    {
        $member = Security::getCurrentUser();
        if ($member && $member->AddressBook()->exists()) {
            $addressoptions = $member->AddressBook()->sort('Created', 'DESC')->map('ID', 'toString')->toArray();
            $addressoptions['newaddress'] = _t('SilverShop\Model\Address.CreateNewAddress', 'Create new address');
            $fieldtype = count($addressoptions) > 3 ? DropdownField::class : OptionsetField::class;

            $label = _t("SilverShop\Model\Address.Existing{$this->addresstype}Address", "Existing {$this->addresstype} Address");

            return FieldList::create(
                $fieldtype::create(
                    $this->addresstype . 'AddressID',
                    $label,
                    $addressoptions,
                    $member->{'Default' . $this->addresstype . 'AddressID'}
                )->addExtraClass('existingValues')
            );
        }

        return null;
    }
Allow choosing from an existing address

@return FieldList|null fields for