@Idham choudry,
you can add below code in to your observer to get customer information.
use Magento\Customer\Api\CustomerRepositoryInterface;
use Magento\Customer\Model\Session;
$this->customerrepository = $customerrepository;
$this->customerSession = $customerSession;
$customerid = $this->customerSession->getCustomerId();
$customer = $this->customerrepository->getById($customerid);
$customer->getFirstName();