Which file should I insert it in?
The theme is "Alpha"
Please tell me who

Write the code of the file to the file to evaluate the link to evaluate the input evaluation.
<?php if(function_exists('ur_button_add')) { echo ur_button_add($user_id = osc_item_user_id(), $item_id = osc_item_id()); } ?>

Depends on your needs, plugin already show buttons via hook so any other placement is upon you.