An extender can only be configured by use of an ethernet cable.
When configuring via a router make sure to have the Config Switch set to 3. Setting this switch will cause the extender to use DHCP even if it was configured with a fixed IP address before. If your computer is also connected to this network you can start to make a connection: Use the Extender Discovery tool which you can find in the Tools menu of ProntoEdit Professional. This tool will automatically open the configuration page of your extender.
When configuring directly connected to the computer, make sure to use a cross-linked ethernet cable and connect via the fixed IP address 192.168.8.80 of the extender. The Extender will now serve as a DHCP server and give your computer an IP address. Typing the following address in your computer's browser will open the configuration page of your extender: http://192.168.8.80/