Would like help understanding buying multiple shares and selling a couple.

Okay, I cannot be understanding this right cause it seems so stupid. I’m in Canada and using Questrade. So if I buy a share of TSLA at $950, the stock goes down to $750, then I buy at $750 and it goes to $850. Can I seriously not sell my 2nd share and make the profit while keeping the first share that’s still down? All I see on the app is an average purchase price of $850. How does this make sense? I really hope I’m misunderstanding. Any help is appreciated.