So basically I have two files I'm uploading right now. The flash.zip that you have to download and the RSD lite zip that is optional.
You need to download the flash.zip or both and extract them and install RSD. After doing so you'll have to put your phone into fastboot by powering it off and holding the power button and vol - key together until it pops up in AP flash. (YOU DON'T NEED TO DO THIS IF YOUR USING THE LAUNCH.bat)
After all of that you need to plug in your phone to your desktop and assuming you have all the drivers installed you need to either open RSD and select the xml in the folder you extracted from the flash.zip and select your phone and start the flashing process.
Now if your phone is not recognized by RSD you need to run the LAUNCH.bat and it will do the whole process in about 5-15 minutes (rough estimate)
After everything is done your phone will reboot and your on 19.5.3 and can root your phone permanently and gain system r/w permissions with my other thread HERE.
Credit for the downgrade through fastboot go to myself and Google for fastboot of course.
Credits for the other stuff in the other thread are in the link up above.