From the beginning:
Go to your e-mail and download the file.
Then, in File Manager, go to the "downloads" folder, it will be there.
From there, open whatever option you have to "move" the file. Maybe press and hold it? maybe there's a menu up top? depends on your device.
Once you select it to move it, go to:
Internal memory (sometimes called internal storage)/Android/data/org.ecmdroid/files/eeprom and put it there (hit OK).
Then, when you go into ECMDroid, go to the menu and hit Eeprom editor, then the three little dots on the upper right and choose "load"
The file you just put in will be there, select it, and the ECM type, then you can "Burn" it to the ECM.
*As long as you already have chosen "Enable ECM burning" in the settings section of ECMDroid
Hope that helps!