1) Why do you want to work with "Enterprise Clients" specifically?
2) What do you think you bring to the table that the other 10 million +++ freelancers do not? Your profile looks (sorry) pretty ordinary...
Freelancers are able to work with Enterprise clients if they come accross a publicly posted Enterprise project in the market place, then they can submit a proposal to that job or be selected by the hiring managers to be invited to be a member of a Talent Cloud network. You can find more information about Enterprise Clients here.
I'm also interested in any tips on how to find Upwork Enterprise clients. I've searched for them, but them seem to be rather ghost-like. Any help would be greatly appreciated!