Thunderbolt 1 to USB Type C adapter?
Use this adapter if it's a Thunderbolt device -> https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter

You will need a Thunderbolt cable as well.  That should work for you, it's worked for me.

If this is not a Thunderbolt device with a USB-C port, but is instead a USB 3.x device with a USB-C port then you need a different cable.  Like this one -> https://www.amazon.com/AmazonBasics-Type-C-Adapter-Charger-Cable/dp/B01GGKYR2O

If you want to get gigabit speeds then make sure it's a USB 3.x cable and not a USB 2.0 cable.

If the device has a captive USB-C cable then there is no cheap solution.  You will need a Thunderbolt 2 dock with a USB-C port, and these are hard to find.  It would likely be cheaper to just replace this USB-C device with a USB-A or Thunderbolt 2 version than get an adapter.