Here is the code:

#include <M5Stack.h>

int last_value = 0;
int cur_value = 0;

void setup() {
M5.begin(); // Init M5Stack.
M5.Power.begin(); // Init power.
pinMode(21, INPUT); // set pin mode to input.
M5.Lcd.setTextColor(YELLOW); // Set the font color to yellow.
M5.Lcd.setTextSize(2); // Setting the Font size.
M5.Lcd.setCursor(80, 0); // Set the cursor position to (80,0).
M5.Lcd.println("Button example");
M5.Lcd.setTextColor(WHITE);
}

void loop() {
cur_value = digitalRead(21); // read the value of BUTTON.
M5.Lcd.setCursor(80, 25);
M5.Lcd.print("Button");
M5.Lcd.setCursor(0, 45);
M5.Lcd.print("Value: ");
M5.Lcd.setCursor(0, 85);
M5.Lcd.print("State: ");
if (cur_value != last_value) {
M5.Lcd.fillRect(85, 45, 75, 85, BLACK); // Draw a black rectangle 75 by 85 at (85,45).
if (cur_value == 0) {
M5.Lcd.setCursor(95, 45);
M5.Lcd.print("0"); // display the status
M5.Lcd.setCursor(95, 85);
M5.Lcd.print("pre");
} else {
M5.Lcd.setCursor(95, 45);
M5.Lcd.print("1"); // display the status
M5.Lcd.setCursor(95, 85);
M5.Lcd.print("rel");
}
last_value = cur_value;
}
}

Thanks in advance.