Scaling out half positions and moving rest positions to breakeven?

I have an AFL in which if I buy 1000 stock at lets say $20 and put the stop loss at the low of the candle which is $19. So the risk is $1 here. I want to sell hald of the stocks (500) at 21 and then move the rest of the stocks cost to breakeven i.e $20
Can you please tell me how to do it ?

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