@CG-7022 Sorry for the delay in response. I was checking on this issue internally with Azure Sphere team, and received an update as below.
Currently, product doesn't support to create a SNMP Manager using PrivateNetworkServices as a template. I have created a feature request on the UserVoice on behalf of you. Request you to kindly provide your feedback and upvote for the same. All the feedback you share in these UserVoice will be monitored and reviewed by the Microsoft engineering teams responsible for building Azure.
UserVoice Link: create a SNMP Manager using PrivateNetworkServices as a template
Do let us know if you need further help in this regard.