How to forbid users to replace attachment after submit expense report?

Summary:

Users can replace attachment after submit expense report

Content (required):

Our users can replace attachment after submit expense report, so the attachment which first approver see may be different from the one which second approver sees. We don't think this function is rational. We want to know how to forbid users to replace attachment after submit expense report?

Thanks in advance!

Version (include the version you are using, if applicable):

23C

Code Snippet (add any code snippets that support your topic, if applicable):