Let's say AAPL current price is $1,000.
I open a new position on AAPL for $2,000 (2 shares) (we'll call this "aapl_1").
At some point later AAPL goes down to $900.
I open a new position ("aapl_2") for $2,000 (2.22 shares).
Sometime later AAPL goes back up to $1,000.
How do I close position "aapl_2" to take a profit, while keeping position "aapl_1" untouched?
I've looked everywhere and it seems there isn't a way to close specific positions, unless they have been opened with a take profit option. I can also use a market order to sell stock, but that will sell a generic number, regardless of the opening price. I can also liquidate AAPL, but that means also closing "aapl_1", which is not what I am after.
What have I been missing?

Thank you