There are a few steps to follow to downgrade a newer version of WordPress to an old version.
Log in to your WordPress admin panel by using wp-admin.
Mouse over on ‘Plugins’
Then click on ‘Add New’
Search for the plugin ‘Wp Downgrade’
Click on install and activate the plugin
Then mouse over on ‘Settings’ and click on it.
Then you can see the target version of WordPress as the version currently installed
In the WordPress Target Version field, enter the release you want to downgrade to.
Then click on ‘Save Changes’
Then you can see the active version of WordPress version
Then mouse over on ‘Update Core’ and click on it.
If anything goes wrong ‘Re-Install’ the version.
That’s all. You can see the downgraded version is the current version of WordPress now.