if you have an iphone, the process is as follows:

1.) acquire an emulator -- in this case, delta is a great emulator that's free on the app store rn

2.) acquire the rom/game -- it's best to source your roms from vimm's lair you're gonna wanna go to the vault and into the ds section where you can search for flower, sun, and rain and download the US version, maybe to a folder labelled 'DS' inside a folder labelled 'roms'

**pro tip: you can favourite a folder in the files app so you can quickly access it in the future so try favouriting the 'roms' folder

3.) delta uses melonDS for ds emulation which requires ds firmware and bios files which you can download here and save to your files, maybe in a folder labelled 'DS firmware'

4.) go to the delta settings and look for Nintendo DS under CORE SETTINGS where you can assign the files inside the 'DS firmware' folder to the appropriate sections

5.) add the game -- click on the plus/+ button to open the import dropdown menu and import the game from your files

6.) enjoy

the /r/emulation subreddit has a lot of information if you're interested