Looks like all you have to do is extract the archive, then enter the directory the files are extracted into. Assuming you need the usb functionality all you have to do is.
The module then gets built and copied to:
Make sure the your usb bluetooth device is plugged in, reboot and the once rebooted it should recognize it, then you can do the following to see if the module is loaded and to see if the system sees the device.
Also check if the bluetooth service is now running and seeing the device, since this is an outdated version you won't have to worry about kernel upgrade so using dkms is not needed.
sudo make install INTERFACE=usb
$ ls -l /lib/modules/$(uname -r)/kernel/drivers/bluetooth/rtk_btusb.ko -rw-r--r-- 1 root root 104216 feb 19 18:25 /lib/modules/5.4.0-52-generic/kernel/drivers/bluetooth/rtk_btusb.ko
lsmod | grep rtk_btusb lsusb