Try this JavaScript below and checkout my blog post on concatenating in dynamics, It will show you how to add this JavaScript as a web resource and get it up and running! Please let me know if this works!
www.clarkandali.com/.../concatenate-in-dynamics-365-with-javascript
//Concatenate Name and formatted DOB into one field
function ConcatenateName() {
//Create a variable for First Name, and DOB
//Name the variables sensibly and set them equal to the field's logical name
var name = Xrm.Page.getAttribute("new_firstName").getValue();
var dob = Xrm.Page.getAttribute("new_dob").getValue();
//Format the date value from CRM to Day/Month/Year
var day = dob.getDate() + "";
var month = (dob.getMonth()+1) + "";
var year = dob.getFullYear() + "";
if (dob != "" && dob != null) {
dob += day + "/" + month + "/" + year;
}
//Create a variable to contain the concatenated values
var nameAndDate = "";
//Create conditional checks for blank or null values
if (name != "" && name != null) {
//Add the name value to the nameAndDate variable
//Add a space afterwards
nameAndDate += name + " ";
}
//Repeat the conditional checks for Date of birth
if (dob != "" && dob != null) {
nameAndDate += dob;
}
//push the concatenated value into the field on the form
//replace new_nameAndDate with the logical name from the form
Xrm.Page.getAttribute("new_nameAndDate").setValue(nameAndDate);
}
