We already covered single user pickers, where you can change that field value based on the user who manually execute it:

• Setting issue Assignee as the user who manually executed scheduled issue

• Set current user as Reporter on manual execution

Now it’s time for multiple user pickers, there are 2 options:

• Set current user in this field on manual execution - on manual execution it will replace all users being mentioned in that field with the user who performs this action

• Add current user to this field on manual execution - in this case, user executing it manually will be added to mentioned users