If you successfully install the FREESWITCH. In this post I will explain how to create the new user or modify the existing user.

Step 1. Locate the conf directory inside the freeswitch installed directory.
Step 2. change directory to default/

 # cd conf/directory/default

This directory contain xml file related to default user extension to be used.
Step 3. To create a new user cp any of the file and name it with your desired extension.

 # cp 1000.xml 9999.xml

Step 4. Make the changes to new file as per your extension.

 # vim 9999.xml 
  change the following tags 
        user id="9999"
choose your password.
        param name="password" value="123"
If you want to change call group make changes in variable tag or default can also work.

 For new group make changes in make changes in default.xml
# vim conf/directory/default.xml 
the file is self descriptive.

Step 5. Make change Regex in dialplan

 # vim conf/dialplan/default.xml 
locate  tag line # 257 
change the regex with your extension number in my case I included 9999

 expression="^(10[012][0-9]|9999)$"

Step 6. Reload the xml file using fs_cli terminal

# fs_cli
freeswitch@internal> reload xml

Its done .... 
Now  test your new extension using your softphone.