Sometime after wordpress update your website breaks, in case you can
still access wordpress admin panel, then following this tutorial you can learn
easily how to downgrade wordpress version to any previous
wordpress versions.

Please take backup before perfomaring any major changes on your website.

Step 1) Install plugin “WP downgrade | specific core version. Click on install now and once installed click activate.

Step 2) Go to settings and click WP downgrade.

Step 3) Choose the specific version you want to downgrade wordpress and after click SAVE CHANGES.

Step 4) Go to Dashboard -> Updates page and then click on “Reinstall version”

That’s all your wordperss will be downgraded to your desired previous version.
if you want to see this tutorial in video format, check here