As per my understanding from your question, it seems you are looking for something similar to this Compute Engine setup [1]. You will need to create a corresponding DNS record in the appropriate zone by using Cloud DNS [2] (you can use a Cloud DNS public or private zone to host the DNS record for the custom hostname). If you were referring to Internal DNS, then you look into this documentation [3].
It is worth mentioning that Google Groups is a place for non-technical how-to questions (where you're likely to find information like service status updates and release notes, and ranging from book recommendations to creative shortcuts) [4].
Therefore, I would recommend you to consider reaching out to Stack Exchange sites [5] (e.g. Server Fault [6] or Stack Overflow [7]) where Google also participates that can help you find answers and troubleshoot problems.
(Please share the step by step instructions on what you have done so far omitting PII/sensitive information and more details about your end goal, so that the community can try to address your query accordingly)