Did you know that Lemmy was created by communists for precisely these reasons? https://en.prolewiki.org/wiki/Lemmy
Or how can we own the existing companies?
Realistically we can only do that by seizing the means of production.
How can the govnments use these companies in a socialist environment?
China and other socialist states are already doing that. The companies there answer to the state, not the other way around like in capitalist states.