1. Please go to your FTP/CPanel, and go to folder "wp-content/plugins"
2. Create a new PHP there and name it with "bp-custom.php". If you already have it, no need to create again. Just open it
3. Paste the snippet on the page and save
PS: On a single "bp-custom.php" file, you only can add one PHP tag code only where it put on the most top of file
<?php
If you want to add multiple snippets, please copy the snippet only.
Alternative
If you don't want to use "bp-custom.php" file, you can use third-party plugin