True! This is the right forum to ask any query but for making changes to the Advertiser (your) account you should contact Adobe Support team. You must be having one Adobe Support address/ Contact to reach out in case of some account related help. If in case you do not find one, please share your Advertiser name and I will get you the address.
Change History Section would only include changes made to the Account settings, for instance Adcopy changes, Budget Changes etc. However to know which user logged in and when did he log in, there will not be any provision in the AMO UI. This information is available at the back end and the support person will be able to provide you with the same.