You need to place 3 trades:
- Buy limit order - 10 lots of Nifty with limit price 50
- Stop limit sell order - 10 lots with limit price at 39 (Place immediately after order 1 is filled)
- Sell limit order - 10 lots of Nifty with limit price 70
Now if order 2 executes first, cancel order 3 immediately and vice-versa.