Go to Exchange and click sell SDI for XMR, click add to cart, view cart and finish your order
To sell Soldi you need a Monero wallet (currently it is the only electronic currency with which you can exchange).
Open your Soldi wallet, enter our SDI address as the recipient, always within your wallet select payment ID and copy it in the Payment ID field, also enter your Monero and Soldi wallet address.
To finish, click Place Order. Your order will be taken over by the system and processed in the following hours, then the sum of Monero will be sent to the specified Monero wallet address.