How to do this command. Im following this article.

https://bastienbaranoff.wordpress.com/2018/08/10/gsm-base-station-with-two-osmocom-bb-compatible-phones-on-kali-rolling/

root@kali:~# osmo-bts-trx -c ~/.osmocom/osmo-bts.cfg -r 99

((*))
  |
 / \ OsmoBTS
There is no such command.
Error occurred during reading the below line:
band GSM900

Failed to parse the config file: '/root/.osmocom/osmo-bts.cfg'

What should I do?