How to replace p#rn with something healthy?

There's nothing inherently wrong with watching porn. Most people do. For the most part, it's a normal and healthy expression of sexuality. As long as you understand that porn is fiction and bears about as much resemblance to real sex as the Fast and Furious movies do to real driving, you should be fine.

You're probably not "addicted" to porn. Can you be addicted to porn? Sure, but you can technically be addicted to anything. Porn is not chemically addictive the way, say, some drugs are. In fact, watching a lot of porn doesn't predict problematic porn usage--but thinking porn is morally wrong does. So basically, you aren't likely to wind up having a problematic relationship with porn unless you already feel guilty for watching it.

An easy way to tell if you are addicted to porn is to ask whether it is getting in the way of other obligations in your life. If you've cancelled hanging out with friends or doing work because you were wanking instead, then it's a problem. But if you just want to knock out a quickie before bed, then there's no problem with it. The only unnatural thing about it is the guilt that centuries of christian culture has pushed onto people.

Porn addiction isn't real. It's the Christians attempting to groom men into shame so they can use it to control you.

Totally normal to be curious/interested in porn. First thing I'd say is to think about what you're watching: does it seem like a healthy thing between two or more people, or is someone being abused or degraded? It's easy to watch a bunch of stuff and get an impression that what you're seeing is normal, but porn caters to various proclivities and they aren't all healthy.

I don't know what to advise about replacing it. You likely have a normal sex drive with no outlet, and expecting yourself to not be horny is probably unreasonable. Fantasy/masturbation without porn might be more reasonable.

Might be worth asking yourself what about it makes you feel bad.

At 19 years it's high time to be curious about nsfw stuff. For most people it starts way earlier than that (from 7 typically), but it takes a while to figure out what it means and what it's safe to do about, even more so in a high-strung environment (which religious people often create).

Consuming porn is entirely normal, and an avenue of exploring sexuality. It's not a very realistic depiction: it's based in reality but about as accurate as getting career guidance from movies. That still leaves plenty to learn about what goes where, explore fantasy, different expressions of pleasure/lust/sexuality, besides the option of choosing material that is more real and/or educational.

If the material isn't appealing to you, feel free to change what you consume. Some porn and some expression might not be for you at this time; some will be from shame or ideas from your upbringing, some will just be from you and your sexuality. Try other topics, other creators, other styles, etc. Maybe it's the amount of penis, or botox, or the impersonality, or the body type, or the lighting, or anything really.

Consider trying different media formats, like video clips, movies, images, but also literature (stories, captions, books), anime/manga, erogames, chat, audio recordings (asmr, audiobooks, dramatisations, recordings), etc. I highly recommend using your own mind as well, daydreaming and/or even more actively exploring fantasy.

Of course also explore your body and responses. It's also a lovely thing to do together with people, and much easier if you can feel relaxed and safe enough with eachother to just explore/try stuff. Use barriers, learn about safer practices, and take care of yourself and eachother as you adventure together.