So you basically want to sell for fiat and then if bitcoin goes lower you buy it back. You use the same amount of fiat but you buy more bitcoin because its cheaper. Sure this is a great way of doing things as long as we are in a bull market. But what will you do if you sell, and the price keeps going higher and higher? Or you sell and it goes lower and lower?

Best is just to hodl if you think it has more growth long term. This type of scalp trading never works out. Especially for new traders. You might get lucky once or twice and get a better average of your bitcoin holdings but eventually you will sell at the wrong time and buy at the wrong time.