How to disable app download ad in Safari

When I log into our company intranet site on Microsoft SharePoint and try to check my email (Outlook online- I know- MS ***** but it's what my work uses) from an iOS device Safari automatically displays an ad at the top of the screen directing the viewer to download the app from the app store.

This is causing some major problems for us as we have over 800 employees and we have to pay $2 / month / user for this app. We want to disable or hide the download option. Our work force is constantly changing (and they don't tend to read the company-wide emails sent out) so even if we were to send out an email telling them not to download it they will usually do it anyway.

Any thoughts are greatly appreciated.