You asked this same question 3 weeks ago.
https://social.technet.microsoft.com/Forums/windowsserver/en-US/dd4194eb-8571-4e35-9b54-9ac22aa5ab2c/how-to-derive-a-machinename-from-a-username-stored-on-a-local-csv?forum=winserverpowershell#dd4194eb-8571-4e35-9b54-9ac22aa5ab2c
Here is a snippet from what you posted in that thread:
<form action="/sessions.csv">
User name (Firstname dot Lastname):<br>
<input type="text" name="$Username"><br>
<input type="submit" value="Submit"><br>
</form>
You cannot post a form back to a csv file. You cannot reference a Powershell variable like $username in this manner. That tells me that you do not have the basic programming skills needed to complete the task.
You need to understand data types, variables, constructs like loops and condition testing, and how to do file I/O.
Essentially, you need to write a small computer program to do the name lookup.
So again I will reply, go get some training. Take a computer programming class at a local school. Take an online course. Or find a programmer in your organization who can help you write this code.
