1. Open the EAC
Click on start and then expand Exchange Server 2016 and click on Exchange Admin Center.
2. Login to the EAC
If you have a certificate warning, click yes to continue and then enter the credentials to login and press enter.
3. Click on Servers
On the left hand side, click on Servers.
4. Double click a server
On one of your servers, double click it to open the properties page, alternatively click the pencil button to edit.
5. Click on Outlook Anywhere
On the properties page, the very last option is outlook anywhere, click on it.
6. Enter your URL's
|Enter in your internal and external URL and select your security option then click Save.