If you didn't keep the output, on the master, you can get the token.

  # on the master
  sudo kubeadm token list

If you need to generate a new token, perhaps the old one timed out/expired.

  #on the master
  sudo kubeadm token create

On the master, you can find the ca cert hash.

  openssl x509 -pubkey -in /etc/kubernetes/pki/ca.crt | openssl rsa -pubin -outform der 2>/dev/null | openssl dgst -sha256 -hex | sed 's/^.* //'

Using the master (API Server) IP address or name, the token and the cert has, let's join this Node to our cluster.

  sudo  kubeadm join --token syvrch.ca1qtym4po3rtxbv --discovery-token-ca-cert-hash sha256:f7c56dbcf2e61c38c2ae0936722195dad2c1851214242lkjflkdsjflksdjflsl

  sudo  kubeadm join $PUBLICIP:6443 --token syvrch.ca1qtym4po3rtxbv --discovery-token-ca-cert-hash sha256:f7c56dbcf2e61c38c2ae0936722195dad2c18512dofisl14242ba4dd8cd119a3deba