Sandbox Instances
Downloading from Sandbox instances is not supported but you can try it by amending the endpoint address in the SF_Download.exe.config file:
<client> <endpoint address="https://login.salesforce.com/services/Soap/u/42.0" binding="basicHttpBinding" bindingConfiguration="SoapBinding" contract="sf_partner.Soap" name="Soap" /> </client>
Change the address to: https://test.salesforce.com/services/Soap/u/42.0. This should work but I’ve not had the opportunity to test it.