If covid virus came from animals, it probably can go back to animals, right? have they tested the pet dogs, cats, or birds of the patients in china?

Unknown: I would certainly think that the WHO would be more concerned about testing humans and finding a vaccine that works and preventing human deaths than spending precious time and resources testing and treating pets.

Maybe, maybe not: Viruses that come from animals don't necessarily infect all animals, only selected species. (We humans may just be unlucky!) There is a single report from China of the pet dog of a COVID patient testing positive, but no report that a pet in turn became the source of a human infection. More research is needed, but probably this won't turn out to be an important problem.