I accidentally knocked off the capacitor on my pocophone

As long as it is definitely a capacitor,no,you don’t need to replace it almost ever,unless you knock multiple off. They are usually there to smooth voltage spikes in a phone. Knocking one off on a line(meaning there are multiple connected together on one copper trace),usually causes very little problems,unless it’s the only one on the line.

But honestly,don’t worry about it if it’s your personal phone.

If it was a filter(basically a wire that helps to block out wireless interference),you’d have to replace it since it completes a circuit,otherwise it’s almost never noticeable.