:-) sure, sorry. I hope, my English will be understandable.
First: Do you have access to your files per FTP? You will need this.
Do you use an own theme? If yes you could put it in the functions.php
If not do this:
Open a text editor like notepad and put this into it:
Plugin Name: My Custom Plugin (any name you like..., must be unique)
Author: Your Name
Description: Customizer Bug Solution (You can write what you want here)
remove_action( 'shutdown', 'wp_ob_end_flush_all', 1 );
Then save this file into your plugins directory: Look for "wp-content" inside your installation and there for the folder "plugins". Save the file into this folder (save it on your computer first and then load it up per FTP) and name it "mycustomplugin.php" (be sure that it doesn't have another suffix/ending and that this name is unique).
O.k. Now open your WordPress site in a browser, login and activate the Plugin on your plugins page.
Please give me feedback if you got it and if it's working for you!