I am not familiar with Minio frankly but a quick look at their docs shows that it is a SDK for working with S3 compatible object server, so you will probably needs to:
import minio library with npm
create a new controller (based on the existing controller) that will take the same data from client side and communicate with Minio instead of S3
match the existing API endpoints to the new controller
Create a new S3 Service (maybe Minio Service) that will talk with minio like the S3Service class does talk with AWS S3
To be able to use it with Minio, what things need to be changed?