In the "Download file" dialog, please check on "Direct path to external SD card". And you can select "Remember Path" to save location for the same file extension in next downloads.
On Android 5 and up, we need to your permission to access SD Card. Please follow these steps:
For the first time accessing SD card from Download Accelerator Plus, a notification appears to request permission. After "Ok", please tap the option at the top right corner of screen to "Show SD Card", then "Recent":
In this menu, please select a SD Card to which you want to grant permission.
Finish all steps by tapping "Select" button. Now you can download files directly to SD Card.
Please note that: Download into SD card is not supported on Android 4.4 due to a restriction by Google. We hope for your understanding!