Currently, it is not possible to update or delete some changelog entities (issue history). It is critical for data anonymization and personal data clean-up. Users and apps can get changelog entities (issue history) using 
https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-issues/#api-rest-api-3-issue-issueidorkey-changelog-get but cannot change or delete some cnahgelog entity because there are no PUT or DELETE methods. 

Why it is important:
1. As a company, we would like to find and clean sensitive content in our Cloud products.
2. Using REST API and some search patterns, we've found that a ticket has not allowed content in history (let's say some SSN or email or customer name).
3. We would like to change this particular changelog entity (issue history) version of a ticket.
4. We can only get changelogs using  "GET /rest/api/3/issue/{issueIdOrKey}/changelog"  (https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-issues/#api-rest-api-3-issue-issueidorkey-changelog-get) but not delete or update it.

As an option, we would like to suggest allowing particular project administrators or Jira administrators to use some PUT and DELETE methods to change or delete ticket changelogs (ticket history).