Value of the counter collide on my lcd while decreasing. How can I remove it?
A simple option would be to call lcd.clear() at the start of loop(). That will clear the entire LCD display. Everything else should work fine because it looks like you're outputting the entire display contents every time round.

Alternatively, you could remove the extra digit by printing a space over it, e.g.:

if (visitor &lt; 10) print(" ");
lcd.print(visitor);


If visitor is a 1-digit number (i.e. less than 10), it will output a space at the start, getting rid of any underlying digits leftover from a previous iteration. If you want the number to be left-aligned then you could print the space after the number instead.