If you installed the Andoid SDK (not Studio) in a different folder than the default (%LOCALAPPDATA%\Android\Sdk).
Edit the
Engine\Extras\Android\SetupAndroid.bat
file to point to your SDK folder.
Ex:
change the line
set ANDROID_LOCAL=%LOCALAPPDATA%\Android\Sdk
to
set ANDROID_LOCAL=C:\Android\sdk
C:\Android\sdk is an example, replace with your path to the Android SDK
Save the file and execute it.