The only way for now (because it's a gba game) is to extract the save of the game (agbsave9), cheat with an emulator on PC, inject the save to 3ds!!
https://github.com/alex34567/Agbsave9
EEPROM support has been added. Most GBA games should work now.
Instructions are the same:
1. Dump save using Agbsave9 and record the title id and save type
2. Open the gen_rom.py script in the agb_inject folder using Python3 to generate a cia
3. In CFW sysnand mode install the generated cia over your gave
4. Run the thing you just installed
5. When "AGB_FIRM save injector" appears exit
6. Go into the Nintendo 3ds folder on you sd card
7. Depending on your cfw setup you will see 1 or 2 folders with random numbers
8. Go into the smaller one
9. Go to the folder in that one
10. Go into title/0040000
11. Go into the folder matching the title id
12. Backup the data folder
13. Reinstall your game
14. Restore the data folder
15. Have fun