how can I find if the model have overfitting

Hello everyone,

I am hoping you can assist me in determining whether my model is overfitting. My model’s accuracy is more than 85%, but when I use new data, the accuracy drops to less than 70%. I have seen suggestions about using a loop, but I am not sure why or how to implement it. If anyone has any answers, can you please explain why and how to do it?

thanks all, any help will be helpful.