how to use aws service account to access S3 bucket in C#

Question

I am trying to access a S3 bucket with C#.

I dont have Accesskey but I have a service account that service account would have an iam role association that would have a policy association that allows it to read from the bucket

I have been asked to use this service account in profile.In lower environments I have setup the same using AccessKey and secret but no idea How to use this service account

Need help here to pass this using AWS_PROFILE variable from environment