Manually: Watching the price and manually clicking when the level is reached. Good if you are an intraday trader, and dont leave open positions overnight. It is not good when price moves violently, especially in crypto, often you will not have time to react.
I find this interesting and it looks like an advise never to leave running market over to the next trading day, this is dangerous. Every trading day has it own challenges so never expect total continuation of the previous day. So close your running trade if on profit or you put stop loss if you are losing before the night falls.
Every day is new, prepare a fresh set up and see direction of the market because if you leave a running to the next day, you will be emotionally confused to take accurate trading decision.
Leaving a trade overnight is still good as long as you set a stop loss as well as take profit, it will just automatically stop if the commands are successfully done. It will only become dangerous if you didn't put those things, and I can't see any reason why anyone would not put those two important things to lower the risk of losing money as much as possible.