Firstly, go to https://addthis.com and create account, if you don't already have one. Once you create account signup for 'Share Buttons' and you will have two code.
1. Copy the first code and paste at Helix Ultimate framework Custom Code > Before </body> as shown below
2. Now go to your template folder and open content php file called 'default.php' using any text editor [templates\[YOURTEMPLATENAME]\html\com_content\article\default.php]
3. Go to Line No 190 and paste your AddThis second code as show below
4. Save and done