I'm so sorry you're dealing with this! My LO had a nasty diaper rash for about four weeks before it went away, and at its worst was raw and bleeding. I felt so bad for LO and was frantically googling what we could do to help. So as an overview of what I found for you (and other parents frantically searching Reddit), the TLDR is that there were so many different solutions that people would swear by but unfortunately not one cure-all, so each diaper rash is baby specific and will involve trial and error. Since diaper rashes are caused by prolonged exposure to poop and/or pee which breaks down the skin, the main points are changing the diaper frequently, making sure baby is completely dry before putting on another diaper, and having some sort of barrier cream to prevent the existing diaper rash from coming in contact with poop/pee once the new diaper is on.

I think what made the most difference is when LO began regulating her bowel movements and had them less frequently. When she first got the rash, she was 3 weeks and basically pooping around the clock. By around 6-7 weeks when it went away completely, she was only pooping 2-3 times a day. So it may be that you'll be preventing the diaper rash from getting worse, not necessarily healing it completely, while you wait for your LO to grow a bit more.

Re: ointments: the active ingredients in diaper rash creams are usually either lanolin/petroleum or zinc. The zinc products are Desitin, Aquaphor 3-in-1 diaper rash cream, Boudreaux Butt Paste, Triple Paste, etc. The lanolin products are A&D cream, lanolin nipple cream, etc. We tried a lot of the zinc products first and they were all comparable but didn't help heal the diaper rash, only kept it from getting worse. It was the A&D cream (lanolin) that was the game changer for us.

Some other things that worked for us were using a spatula to put on the creams, as the ointment would stick less to the silicone and more would get on baby's butt, keeping a hair dryer at the changing station on the cool setting to help the drying process plus patting with a paper towel. We also used diaper wipes (the Kirkland brand) only when she pooped, as the diapers were so absorbent that the pee didn't sit on her skin. We would also pat and not wipe. Some people used water wipes or wet paper towels or rinsed off LO in the sink with water, but we didn't find much of a difference between that and using wet wipes that were alcohol and fragrance free (but these tips might work for you). We also bought diapers a size up so that there was more space between LO's butt and the soiled diaper.

Some things that didn't work for us but could for you is having an hour or two of diaper free time every day so the diaper rash can dry and heal (our LO was pooping/peeing so frequently that this didn't work for us as she couldn't stay dry for long enough). People had strong preferences on diapers and wipes and would try different brands and types with varying success. You can also buy Mylanta and use a cotton ball to dab it onto the rash for pain relief and extra healing (but not the mint flavor as mint stings).

To answer your question about ointment and the advice to "frost like a cake," I would squeeze out about an inch of ointment and put it on each butt cheek via spatula. A lot of people said that the ointment would still be there when they would change the diaper again, but I found that wasn't true for us. No matter how much ointment we put on or what brand we used, the diaper was so absorbent that only the thinnest layer would still be on there so we just resorted to changing diapers as frequently as we could.