Do you own it or does the company?
I’ll assume you are asking about what happens to your saliva sample.
There are a few things that companies do, but mostly… it is destroyed.
Unless you’ve given your explicit consent that your sample can be stored for any future analyses or research, then your sample is destroyed upon processing. Storage of such samples is expensive and companies don’t want to spend the money for this. There are a few exceptions, for example if your sample is part of a trial or a clinical study and thus has clinical relevance, then it might be stored for future use. But in any case, you would have read and signed a consent form.
The digital “evidence” of your sample should be available to you and it is also available to the company (in most cases) and to other third parties like researchers (only upon prior consent from you).