Okay. The cheapest way is using the presets available in the Photos app on iPhone or iPad. There are two for making photos look colder (more blue). In addition to those, you can make your own changes. It has a good amount of adjustments, but you can’t save them as new presets.
If you want to have more choice, I would suggest looking at Pixelmator Photo for iPad. The price is 10 USD as a one-time payment. Then you will have many pre-made presets mimicking old analog film photo styles. You also can make a ton of different manual adjustments.
If you create a style you like, you can save it as your own preset. Creating presets is very easy in Pixelmator Photo. Once you have your personal style preset, applying it is as easy as opening a photo in editing mode and tapping the preset.
When you are feeling lazy, there are plenty of machine learning supported enhancements that often do a good job. One of them changes a lot of different settings and sometimes the results are astonishingly good. Other useful ML adjustments are auto-cropping and auto-straightening.
One of the newer features is called ML Super Resolution. What it does, is make your images higher resolution and also sharper. It’s a niche feature, but if you want to magnify details of a photo beyond its original resolution, this is incredible.
The latest enhancement is in how you change curves in photos. Traditionally you push the line in a graph to adjust the tone in the photo up or down. With On-Image Curves, you tap the area in the photo that you want to change, and slide your finger up or down to change the tone curve for that area. It is very intuitive compared to “the old way”.
There are many more things to say about Pixelmator Photo, but I can’t mention them all. 🙂 In my opinion, as a former photographer, it is an app for beginners and professionals alike. You can grow with it.
I used Adobes Photoshop Lightroom for many years. Primarily on a Mac, but also on iPad and iPhone for a few years. It, too, is a very good tool. It supports a photographers workflow very well and is made for editing hundreds or thousands of photos in one session. That said, it also has a steeper learning curve.
I stopped using Lightroom when there were equally good alternatives that also was considerably cheaper. Adobe has a subscription model that I’m not very fond of. They rely on their corporate customers to stick with them because for many years they have been the gold standard of image creation and editing. That comes at a premium. They were not very fast developing great tools for iPhone and iPad, so other smaller companies managed to beat them in usefulness on iOS and iPadOS.
Now Adobe has many great tools for iPad. You can use Lightroom for free with some limitations, so try it out if you are curious. I have both, as well as Pixelmator (the standard edition) and Serif’s Affinity Photo, but use Pixelmator Photo 50 times for every time I use any of the other.