This process is meant to increase the size of Tesla by $500M, by simply putting $500M into its bank account. The people who are providing this money are getting new shares in return. In theory, the value of the new shares should be $500M, and the value of the old shares should add up to the old market cap of the company, and the sum of the new shares and the old shares will naturally add up to the company's new market cap.
There are second-order effects, though. If there is only a fixed demand for Tesla shares, this may reduce the price of shares (and so devalue the shares of existing shareholders.) Conversely, if people think that Tesla is going to make very good use of any new money, then existing shareholders may end up better off.