How can I train the neural network for an another input set, without losing the learning of the previous input set?

Please somebody answers this. I read this tutorial (https://hmkcode.com/ai/backpropagation-step-by-step/) about backpropagation. So using this backpropagation we are training the neural network repeatedly for one input set, say [2,4] until we reach 100%accuracy of getting output as 1. And the neural network is adjusting its weight values accordingly. So once after the neural network is trained…