Take a look at the Magento\Sales\Api\CreditmemoManagementInterface::cancel method and at the Magento\Sales\Api\CreditmemoRepositoryInterface::delete methods. First you should get your creditmemo using Magento\Sales\Api\CreditmemoRepositoryInterface::get($id) method. Then use Magento\Sales\Api\CreditmemoManagementInterface::cancel($id) method to cancel it and Magento\Sales\Api\CreditmemoRepositoryInterface::delete(\Magento\Sales\Api\Data\CreditmemoInterface $entity) to delete. In theory your code should looks like this:

class DeleteCreditmemo
{

    public function __construct(
        \Magento\Sales\Api\CreditmemoManagementInterface $creditmemoManagement,
        \Magento\Sales\Api\CreditmemoRepositoryInterface $creditmemoRepository
    ) {
        $this->creditmemoManagement = $creditmemoManagement;
        $this->creditmemoRepository = $creditmemoRepository;
    }
    
    public function deleteById($id)
    {
        try {
            $creditMemo = $this->creditmemoRepository->get($id);
            $this->creditmemoManagement->cancel($id);
            $this->creditmemoRepository->delete($creditMemo);
        } catch (\Exception $e) {
            // something went wrong
        }
    }
}

Take a look at the Magento\Sales\Api\CreditmemoManagementInterface::cancel method and at the Magento\Sales\Api\CreditmemoRepositoryInterface::delete methods. First you should get your creditmemo using Magento\Sales\Api\CreditmemoRepositoryInterface::get($id) method. Then use Magento\Sales\Api\CreditmemoManagementInterface::cancel($id) method to cancel it and Magento\Sales\Api\CreditmemoRepositoryInterface::delete(\Magento\Sales\Api\Data\CreditmemoInterface $entity) to delete. In theory your code should looks like this:

class DeleteCreditmemo
{

    public function __construct(
        \Magento\Sales\Api\CreditmemoManagementInterface $creditmemoManagement,
        \Magento\Sales\Api\CreditmemoRepositoryInterface $creditmemoRepository
    ) {
        $this->creditmemoManagement = $creditmemoManagement;
        $this->creditmemoRepository = $creditmemoRepository;
    }
    
    public function deleteById($id)
    {
        try {
            $creditMemo = $this->creditmemoRepository->get($id);
            $this->creditmemoManagement->cancel($id);
            $this->creditmemoRepository->delete($creditMemo);
        } catch (\Exception $e) {
            // something went wrong
        }
    }
}

UPDATE:

/**
 * Cancel an existing creditmemo
 *
 * @param int $id Credit Memo Id
 * @return bool
 * @throws \Magento\Framework\Exception\LocalizedException
 */
public function cancel($id)
{
    throw new \Magento\Framework\Exception\LocalizedException(__('You can not cancel Credit Memo'));
    try {
        $creditmemo = $this->creditmemoRepository->get($id);
        $creditmemo->setState(\Magento\Sales\Model\Order\Creditmemo::STATE_CANCELED);
        foreach ($creditmemo->getAllItems() as $item) {
            $item->cancel();
        }
        $this->eventManager->dispatch('sales_order_creditmemo_cancel', ['creditmemo' => $creditmemo]);
        $this->creditmemoRepository->save($creditmemo);
    } catch (\Exception $e) {
        throw new \Magento\Framework\Exception\LocalizedException(__('Could not cancel creditmemo'), $e);
    }
    return true;
}

So you can reproduce & use same logic as in the method in your own model, but this is not a right way... In any case, I hope this information will be useful to you.