Hi,
this you see in the manual
str_replace
Replace all occurrences of the search string with the replacement stringstring str_replace(search, replace, subject)
"Search" is "." (the dot)
"Replace" is "" (empty)
"Subject" is your question "birth"
So: {str_replace(".","",birth)}
But you did not say, what type of question do you use to capture the birthdate.
We assumed it is a "short text". If you use a "date/time" question it is different, as this question type stores dates as "YYYY-MM-DD".
Here you may use
{str_replace(".","",birth.shown)}
Joffm