I think some of your text is missing 🙂
But you can resolve this by logging in to the AirWatch console > Administration > AW Tunnel Proxy > Certificates tab
Click on edit for the certificate that is being used by the service, in the cert dialog box, select sha256 with rsa encryption for the signature algorithm and then click save
You will need to restart the AirWatch Tunnel Proxy Service afterwards. And for clustered AirWatch environment, you will need to update it on all of the nodes in the cluster.