You may find this helpful https://www.hometalk.com/1082403/homemade-toilet-bowl-cleaner
Hi Dorothy: Baking soda and vinegar are two of the most useful household products that can be used to clean many things, including hard water stains in the toilet. ... Add about 1 cup of baking soda to the toilet bowl, then add another 1 to 2 cups of vinegar. This will create a fizzing action. After the fizzing stops, scrub with the toilet bowl brush and flush. Good luck
Forget baking soda. I live in Las Vegas, where water is extremely hard and forms a ring around the toilet. I have tried everything for 16 years. I now use a pumice block. It is so amazing. It’s been at least 3 months, nothing has formed around the toilet. I just clean with a brush, once a week.
Make a paste of baking soda and hydrogen peroxide and apply to your toilet surface. Let sit for 1/2 hour or so and then scrub thoroughly with a scrub brush. Repeat as necessary.
Here is a great video that shows how to do it with baking soda and vinegar: https://www.youtube.com/watch?v=ZucsFQHdCKE
Drain the water from the bowl. Apply the baking soda straight or making a paste of baking soda and hydrogen peroxide. Then scrub and rinse.
Just make a paste and with gloves spread on the side of toilet bowl and use your toilet bowl brush to clean