This is paraphrased from someone else's answer that helped me. I added a few notes...
You'll essentially be going back to an earlier beta for a little bit, but you can update back at the end. This could take a while, and you may have to fully wipe your phone once on the earlier beta if you cant get the watch to pair.
YOU MUST BACK UP YOUR PHONE BEFORE THIS!!
1. Download iOS 13 beta 5 from the internet (A moderator has to approve this post if I include a link so the site I found is called iPod Hacks 142. Click on iOS -> iOS 13 -> scroll down to Beta 5 and use that one)
2. Choose your phone on the website and wait for download
3. Connect your phone and open iTunes (or Finder if you have Catalina on your Mac)
4. Once you are in your phone's menu, hold down the “Option” key and then click on “Update”
5. Choose downloaded file of iOS
6. Wait for update to complete
7. Connect to your Apple watch and update the watch to the newest software before your phone.
Last question, can I use Window laptop to complete above process?