You can get the APK file from the download link that is sent to you by the Administrator.
Alternatively,
If you know the hostname/ip address of the server you can download the APK file by accessing the link as below.
Eg:
http://<hostname of the server>:10443/Setup/emss.apk
http://<ip-address of the server>:10443/Setup/emss.apk
Alternatively,
You can also find the link for downloading the APK under "eScan Client Setup (Android)" on the login page of the console which can be accessed from the links as below.
http://<hostname of the server>:10443/Setup/emss.apk
http://<ip-address of the server>:10443/Setup/emss.apk