I have method that run another private method in foreach

Here is main method

 public async Task<IList<IssueResponse>> GetIssuesAsync(string query, string email)
{
    var fields =
        $@"key,summary,description,status,issuetype,updated,created,attachment,assignee,reporter,
            {IssueFields.RequestType}, {IssueFields.ApproversField},
            {IssueFields.MinimumNotificationsReportersField}, {IssueFields.MinimumNotificationsUsersField},
            {IssueFields.StandardNotificationsReportersField}, {IssueFields.StandardNotificationsUsersField}, {IssueFields.StandardNotificationsAssigneeField},
            {IssueFields.FullNotificationsReportersField}, {IssueFields.FullNotificationsUsersField}, {IssueFields.FullNotificationsAssigneeField}";

    var expand = "renderedFields";

    var queryParams = new Dictionary<string, string>
    {
        { "jql", query },
        { "maxResults", "100" },
        { "validateQuery", "false" },
        { "fields", fields },
        { "expand", expand }
    };

    var request = this.ConfigureGetRequest("search", queryParams: queryParams);

    var result = await this.SendRequestAsync<IssueListResponse>(request);

    var issues = result.IssueList;

    foreach (var item in issues)
    {
        item.Fields.Attachment = await GetAttachments(item.Key, email);
    }

    return issues;
}

As you see in foreach I have call for another method

Here it’s code

 private async Task<List<IssueAttachment>> GetAttachments(string issueKey, string email)
{
    var attachmentRequest = this.ConfigureGetRequest(issueKey, this.settings.GetAttachmentsPathUrl).AddXClientHeader(email);;

    return await this.SendRequestAsync<List<IssueAttachment>>(
               attachmentRequest,
               new List<HttpStatusCode> { HttpStatusCode.OK });
}

How I can use Task.WhenAll to get attachment in parallel?