String to date conversion

I am inputting a date field, manipulating it, and then want to out put it in anotherdate field

I first parse the date, manipulate into a string. My conversiom of that string to date is not working. It seems to be producing another string variable.
Here is my code and output

//{newdate} is the manipulated field
{newdate} = {currYear}."-".{fillMonth}."-".{fillDay};

$nd = {newdate};

echo " Phase I nd = $nd ", “
”;
$typ = gettype($nd);
echo " Phase I nd is type ", $typ, “
”;

$date = strtotime($nd);
echo " $ date is ", $date, “
”;
$typ = gettype($date);
echo " Phase I date type is type ", $typ, “
”;

$ddd = date(‘Y-m-d’, $date);
$typ = gettype($ddd);
echo " $ ddd is ", $ddd, “
”;
echo " Phase I $ ddd type is type ", $typ, “
”;

My output is:
Phase I nd = 2021-05-19
Phase I nd is type string
$ date is 1621396800
Phase I date type is type integer
$ ddd is 2021-05-19
Phase I $ ddd type is type string

Can anyone help?

There is An example macro in even onload on the right. I think you van use that for tour project

I’m sorry, I dont see where