Check this box and select Apply, then confirm, and all of your positions will be reset to zero and your account net liquidation value will be set back to $100,000.

Click it and a window will appear where you can either set the account cash or, check the box to 'Reset All Balances and Positions'. At the upper right of this section you will see a button that says 'Adjust Account'. Once an account is selected go to Monitor>Activity and Positions>Position Statement.

To reset your PaperMoney account back to its default values, you would first need to select the an account from the account drop down at the upper left of the thinkorswim software (it can't be on TOTAL ALL ACCOUNTS).