TomTom Rider uses the USB Media Transfer Profile (MTP) for transferring routes. On a Mac you need to install a program that supports USB MTP, such as Android File Transfer.
Once the program is installed, connect your Rider 40/400 to your Mac and select Import routes. This switches the device to MTP mode. Route files such as GPX and ITN can then be copied to the internal memory of your device or a memory card using the MTP program.
If you are using Windows XP you may need to install the Media Transfer Protocol Porting Kit in order to transfer routes to your device.
For Windows Vista, 7, 8 and 10 there is no need to install additional software in order to transfer routes. When your device is connected to the computer, you can find it listed as a removable drive in Computer. You can then manually copy routes to the device or import them using Tyre.