The input in the Splunk Add-on for Microsoft Office 365 is a modular input, not a monitor input. So you can not use splunk edit monitor to disable it.
To disable it, there are three ways:
1. you can open the inputs.conf and put disabled=1 under the stanza
2. go to the Web UI -> Settings - Data Inputs -> Microsoft Office 365 Message Trace -> Disable
3. go to the Web UI then go to the Microsoft Office 365 Reporting Add-on for Splunk -> Inputs -> Action -> Disable