Need help building an EA -- What function is used to modify an open position

[Neal_Van]

In an Expert Advisor... What function is used to modify an open position of the chart / symbol that the EA is located on?

Thank you!  

[Neal_Van]

Anyone please.... 

[Marco vd Heijden]

Neal_Van:
Anyone please.... 

Please visit https://www.mql5.com/en/docs/trading

[Neal_Van]

Marco vd Heijden:

Please visit https://www.mql5.com/en/docs/trading

Yes, I read them.. But still confused.  I need to know which function or functions to use to modify an open position and change the stop loss price?