In order to install package control you can visit this page and follow the instructions: Sublime Install package control
Select the first file for comparison to be active.
How to install Compare Side-By-Side(check below how to install package control):
This will open the Find and Replace Console at the bottom of the window.
To find and replace all matches in a single file, press the key combination CMD + OPT + F on macOS and CTRL + ALT + F on Windows and Linux. In this tutorial, we will go through how to find and replace single and multiple matches with Sublime Text 3. Both provide simple text, case-sensitive, whole word and RegEx matching.
Sublime Text 3 has two built-in find and replace functions, one for searching in a single file and another for searching multiple files in a directory.