You may click “Trade” to check your current Positions. There are two methods to close your position:
1. You could click "Limit" to make a limit order, or click "Market" to make a market order under the "Close Position" option to close your current position.
2. You could make an opposite position to offset your current position.
For example, Emilia holds a long position of 1000 contracts. When she makes another short position of 1000 contracts, the two positions will be offset and the long one will be closed.