If you really mean a formula, meaning you will retain the dotted values and
display the number without the dots in another cell, then use this
formula...
=SUBSTITUTE(A1,".","")
If, on the other hand, you are trying to modify each cell's value in place,
then you can use Edit/Replace from Excel's menu bar... put a dot in the
"Find what" field and leave the "Replace with" field blank (empty).