Some time ago, when SBD price was skyrocketing steemit removed option to convert SBD into STEEM becasue it was unprofitable for. It was better to sell it directly on the steem market or on external exchanges like bittrex or binance. SBD is abbreviation for Steem backed dolar so for 1 SBD we should get the steem worth exactly 1$. Now when Steem is worth less than 1$ for 1 SBD we should get around 3-3.5 steem. But since Steemit removed option to convert it here we have to use external services like steemconnect. Simply put your replace placeholder with your nickname and open link in your browser. https://steemconnect.com/sign/convert?owner=place_holder&requestid=1&amount=1.000%20SBD also change amount to the desired.
Best Regards :-)