Display a value in a ConnectIQ graph Title

If I understand, in settings you want to display the string where you replace (5) with the current value?

You can't do that.  When you have app settings, a json file is created with the strings, that gets included in the iq file, and when a user wants to change settings, that info is pulled from the app store.

Actually I want to have the graph title in the Garmin app after my ride to be "Puissance moy. est. lis. (5) "
Where five is the value defined by the user in the setting of the datafield

That's easy if you mean you just want to replace the (5) with your value

var str="substitue this (5)";
var yourValue=123;
var newStr="";
var i=str.find("(5)");
if (i!=null) {
	newStr=str.substring(0,i)+yourValue;
} else {
	newStr=str+" "+yourValue;
}
System.println(newStr);

And the output is

substitue this 123

in the event (5) isn't found, it just adds the value at the end...

You can't do that, because the title is the static string in your XML. The only difference users will be able to see between them is the language.

Correct if this is for displaying fitContrub data.  Like app settings there's json files in the iq file that are used to display the data, and when Garmin Connect displays fitcontrib data, the json is pulled from the app store and is used to display it