This may be a simple question but I am having a hard time figure out how to add Last Name on Sort by in People search. 

![enter image description here](https://i.stack.imgur.com/zIa0t.png)

Any help is greatly appreciated. 

Thank you for reading. 

//Update - tried to follow suggested instructions but I am not able to modify the xsl 

![enter image description here](https://i.stack.imgur.com/Ed3KT.png)

Tried to edit "people Search Core Results" web part and that is showing xsl editor/code however, I can't find the tag. 

```
<xsl:for-each select=”$results”>

```

Any help is greatly appreciated.