There are cases when multiple individuals work on the same work item. It can be pairing, mobbing or other practice. By design, a Jira ticket has only one assignee. Below are the steps to configure "multiple assignees".
1) Add a custom field
2) Enable "Multiple Assignees" feature
Add a custom field of the "user" type that accepts single or multiple values. You can use any name, we recommend using the name that better reflects your use case. The user interface may vary depending on the Jira project type.
Enable "Multiple Assignees" feature
In project settings, enable the "Multiple assignees" feature and select the custom field from the dropdown.
It is important that members of the team are aware of this field and use it consistently. Here are some tips:
Make sure this field is visible in the common views
Use automation to create rules to populate this field