Unless a plant is already injured I doubt even undiluted 3% H202 would do much damage to it. Plants have very advanced antioxidant "systems" to endure sitting out in the sun all the time. What sort of damage are you seeing?

I have seen very low dilutions of H202 for sale in a garden shop for $15 a bottle and laughed at how absurdly overpriced it was. I can't even remember what they are supposed to treat. Part of the issue though, is the producers have to pay for EPA registration, so it's not quite as simple as putting some very dilute H202 in a bottle and selling it. (but still not justifying a 100X markup. Of course it is also OMRI certified, since dilute hydrogen peroxide is pretty benign and therefore acceptable for 'organic' agriculture)

What pests are present?

Davidrt28 I kinda figured they would be fine I just wasn't sure haha. I'm new to growing anything lol. That's ridiculous that a premade solution is $15 it's pathetic, but that's companies and the economy for ya. And the damage I saw was quite a few leaves would just have a little yellow hue and they'd be pretty weak, a tiny breeze would be enough to make those yellow leaves fall off the plant. Even some leaves that were really green and healthy looking just snapped off the plant with very little wind, some were very limp and brittle though, they kinda looked as if it would be really thirsty for water, but not on all the leaves only certain individual ones. And hydrogen main use is to help with any fungal infections going on with the soil or certain infections within the plant itself. And it's also a good fungus gnat larvae killer.

Tiffany, I currently have fungus gnats and thrips, but I was using the hydrogen peroxide to help with the fungus gnats and to mainly help treat some powdery mildew on some of my plants.

It sounds like these plants may not be worth bringing inside. BTi will kill fungus gnats, if you want to bring a pot of dead bugs into your house. Rooting some fresh cuttings could be a way to keep the plants, keeping only vigorous young versions thereof if the plants are currently healthy enough to do so. Once that is accomplished, I would toss the old roots/soil in the garden and use fresh soil.

Tiffany, yeah I was thinking it wasn't really worth it. But I live in Saskatchewan Canada, and I haven't gotten any peppers this year yet. It's already getting really cold outside, I'm pretty sure we had 1 or 2 nights of frost already maybe just 1, but my peppers are still green. I was wanting to try and put them in my shed with a cheap grow light just so I can at least get 1 pepper for seeds this year, I'm just not sure if it'll be warm enough in there. I would try repotting them into brand new soil and continue to grow them, but I don't have any indoor growing equipment. I have noticed that the powdery mildew is like completely gone now lol. I did prune them as well to help them get more airflow to all the foliage and the peppers.

I can totally relate to all of that. I'll be bringing a ridiculous amount of plants inside when frost threatens.

Tiffany, I actually just found out that I'm not allowed to over winter my plants inside. My mom said that she doesn't want any outdoor plants coming into the house. So all I can really do is just wait and see if the weather outside will be good enough, to keep these pepper plants alive long enough to get some good peppers.

Understandable. If possible, put them against a south-facing wall unless that happens to be a mostly shady area. Best luck! It's great that you're going through this learning phase with plants so early.