Hi,
I ran a speedtest and the network provider was "Microsoft".
If you speak about testing network speed using https://www.speedtest.net then it is complex and makes no sense, since any solution will reduce your speed as it will be using a provider between Microsoft network and the fake network which the provider will provide
speedtest.net get the IP of the machine you use and from the IP then know who is the provider - this is an open information (IPs are mapped to specific countries and Internet service provider (ISP)
You can send speedtest.net a "fake information" if you pass all your traffic through a different machine which is located for example in different country and uses different IPs and if your machine is not exposed to public but only uses internal network like VPN.
A simple solution for example is to use proxies.
For example, you can use TOR. TOR is free and open-source software for enabling anonymous communication. It directs all your Internet traffic through a free, worldwide, volunteer overlay network.
https://en.wikipedia.org/wiki/Tor_(network)
Do the test using TOR and you will get the IP of the proxy which you use but the result of the test will be poor since you directs all your Internet traffic through other machines/networks and you will get their speed nd not your original speed