Cognito - Checking Existing User

I have created user pool and adding users to the pool by logging in through the AWS console. When I add a user to the pool, the confirmation status set to "force change password". And an email is get sent to the user email address with a temporary password.

I have built a ReactJS application where I want the user to set their own password. And I intend to use the following workflow in setting their own password.

1.User is on the forgot password page --> 2.user enters the email address --> 3.if user exists, an email is sent to the email address with unique code --> 4.simultaneously user redirected to a page, where user can enter the code and new password.

In the 2 step, where user enters the email address, I have used the following to code to validate if the user exists in the user pool.

import UserPool from "./UserPool";
import { AdminGetUserCommand, CognitoIdentityProviderClient } from "@aws-sdk/client-cognito-identity-provider";


export  const getUser = (email) => {
    

    return new Promise( async (resolve, reject) => {

        const input = {
            UserPoolId: UserPool.getUserPoolId(),
            Username: email
        };
        
        const client = new CognitoIdentityProviderClient({
            region: region_name_here
        });
       
        const command = new AdminGetUserCommand(input);
        
        const response = await client.send(command);


    });
}

But this piece of code throughs an error. Specifically in the "CognitoIdentityProviderClient", which says "credentials are missing". Can someone let me know what I am doing wrong in here please ? And I need to know how I can use that temp password and set an own password for the users.