I have seen on various sites and on youtube videos pertaining to the terraform of various planets and moons that are not habitable for now but they can be habitable in near future. What are the ways through which scientists can do this impossible task as we all know that Triton (Neptune's moon) have nitrogen dominating atmosphere and also consists of methane and carbon monoxide.
TL;DR: Looking at the conditions of Triton and the current technology we have, it is almost impossible to terraform Triton.
It is hypothesized that Triton could be used for colonization. Its surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water. BUT, BUT.... but don't get excited. It is very cold outside. Its surface temperature hovers around 35 K-38 K which is roughly -235 °C, not hot enough to melt the frozen nitrogen, methane ice and water-ice unless you want to extract the the thick water-ice and solid nitrogen that shoots out of the cryovolcanoes of Triton. Also you can see rivers of methane flowing around just like rivers on Earth. So, the surface is kind of different than what is on Earth. Instead of dirt, rocks, pebbles and solid ground, you have to deal with frozen nitrogen, frozen carbon dioxide, ice as surface.
Now, look at the atmosphere. You have a nitrogen atmosphere and trace amount of methane and ethane vapor that forms clouds and condenses into snow, dew, and rain. Now you might be thinking: "Hmmm...those are greenhouse gas!!, we want want to use it to heat the atmosphere. The nitrogen and methane will melt and eventually starts boiling in the atmosphere trapping the heat in the already thick atmosphere. Sounds great!!!". Well you can but it is not only easy but it is catastrophic. The idea of warming the surface or atmosphere of Triton to human norms is pretty much off the table as a terraforming approach. The temperature shift is just too enormous to attempt, and would catastrophically change the entire atmosphere. Besides, we don't have the technology to make the artificial heating source to make such large changes in atmosphere.
Another possible approach is to drill down to Triton's liquid-water oceans under the frozen crust and warm the ocean water as if we are establishing an ocean-floor colony. But this is also by no means easy. We have that level of scientific understanding to make it possible but we don't have the technology and resource.
On another note, how can you make breathable oxygen?
If technology advanced to the point that tapping geothermal energy is possible, it could make a colony of cryogenic world in Triton feasible, supplemented by nuclear fusion power.
You can read the following articles for more info: