Sorry to bother the forum again. I stated that I solved the echo problem by increasing the hertz value in the tuning settings. The 460 Hz value caused the piano to produce a clear but very high-pitched sound. Although I was happy that my echo problem was resolved at first, the sound I heard later disturbed me. Then I set the hertz value to a value lower than the standard value of 440 hertz, the echo disappeared again and I started to hear a more saturated sound. My teacher also liked my new setting. As a result, if anyone has an echo problem, they can solve this problem by changing the hertz value.
* Please forgive the spelling mistakes as I wrote it with a translate program.