No funds are stored on your account at The Sandbox.
Your funds and NFTs are already stored in whichever wallet that you connected to your account on The Sandbox when you registered. There is no such thing as a "Sandbox wallet".
The $SAND user interface on our website is simply showing you how much $SAND is in the wallet that you connected to the account.
Your funds and NFTs are in whichever wallet that you connected to your account when you registered. It is your sole responsibility to remember and keep safe your cryptocurrency wallet credentials and the tokens inside that wallet.
If you registered with an email address, you likely have a Bitski wallet (https://www.bitski.com/).
If you registered through the Web3 option, you likely have a MetaMask wallet (https://metamask.io/). (Or a Brave wallet if you use the Brave browser).
If you registered through the social networks option, you likely have a Venly wallet (https://www.venly.io/). (Note that Venly was previously known as Arkane).
Use the links above to access your wallet. When you have accessed your wallet, there will be tools within it to withdraw your tokens.