I want to revert back to MAMP PRO 4.5.

You can revert back to MAMP PRO 4.5 by downloading it here

https://www.mamp.info/en/downloads/older-versions/

Note: Please make a backup of /Library/Application Support/appsolute/MAMP PRO/db  folder and your host files as well before proceeding.

1. Remove your /Applications/MAMP PRO.app application.

2. Install MAMP PRO 4.5 over your current installation of MAMP PRO 5.xx. DO NOT use the uninstaller in your MAMP PRO menu, this will delete your database data.

3. Rename your /Library/Application Support/appsolute/MAMP PRO/db/mysql56_2018-XX-XX folder to /Library/Application Support/appsolute/MAMP PRO/db/mysql56

4. Rename (or remove) your /Library/Application Support/appsolute/MAMP PRO/db/mysql57 folder. This is your MySQL 5.7 upgraded data which is to be used in MAMP PRO 5.

Your MAMP PRO 4 (MySQL 5.6 data) can be found in /Library/Application Support/appsolute/MAMP PRO/db/mysql56

5. Delete the file: Users/username/Library/Preferences/de.appsolute.mamppro.plist

Note: If you open MAMP PRO 4 again, and receive a warning, specifying a mismatched MAMP.app, then re install MAMP/MAMP PRO 4 again (the installer did not install a matching MAMP.app in /Applications/MAMP, which is causing the problem). When the installation is done, you should be able to start MAMP PRO 4 and start your servers.