If you would like to convert your remaining non-base currency balance(s) into your base currency in Trader Workstation (TWS), you can do so easily from your Account window. In TWS, click the Account menu option followed by Account Window. Scroll down to the Market Value-Real FX Balance section. Right click on the balance you wish to close and choose either "Close Currency Balance" to set up a closing order for that currency or "Close All Non-base Currency Balances" to set up closing orders for all of your non-base currency balances. Once you have made your select, you will now see the order(s) on your screen ready for submission.
You can read more about how to close out currency balances through the TWS Account Window in the MEXEM Knowledge Base.

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Please Note: If you do not immediately see your orders, go to the Pending orders page in Classic TWS to see the created orders. You will likely need to review these orders and transmit them before they are submitted for execution The use of a market order when performing a currency conversion may result in an order rejection due to margin requirements. A limit (LMT) order may help you to avoid this. The limit price is the worst price you are willing to trade at; if a better price is available your order will be executed at a better price In case there is no direct pair between the currencies, such as in between CHF and HKD, then to convert your balance from one currency to the other, you will need to use a common currency.

See also: I am unable to find the desired currency pair MEXEM will act to automatically convert non-Base Currency balances only where the balance is nominal (i.e., below USD 5 equivalent and assuming no subsequent trade activity through settlement) and when the customer requests to close the account (where the balances are below USD 1,000 equivalent).

More details may be found in the MEXEM Knowledge Base.
If you are in the MEXEM Mobile app, you can use the Convert Currency feature accessible from the main menu in the top-left of the screen.
Currency balances will not necessarily match the Virtual FX Positions created to track P&L on Forex orders.

See: How do I get rid of a Virtual FX position?