The search function in NIMAX doesn't always find instruments. To connect to your scope, navigate to Devices and Interfaces in NIMAX and select Tools. Hover over NI-VISA and select VISA Interactive Control. This will open a new window and you can enter in the scope identification in the Resource to Open bar. The identification will be in the format "USB::Vendor ID::Model ID::Serial Number::INSTR". You can find this information for your scope under Utility > I/O > USB Device port. Once you have typed in the ID, hit enter and this will open the Interactive Control window and allow you to communicate with your scope.