using (var context = this.sharePointOnlineAuthenticationHelper.GetClientContextWithAccessToken(siteUri.ToString(), siteToken))
{
    var site = context.Site;
    context.Load(site, s => s.Audit, s => s.AuditLogTrimmingRetention, s => s.TrimAuditLog);

    context.ExecuteQuery();
    site.TrimAuditLog = true;
    site.Audit.AuditFlags = AuditMaskType.All;
    site.Audit.Update();
    context.ExecuteQuery();
}

private static void setAuditReportLibrary(String targetSiteUrl)
    {
        using (var ctx = new ClientContext(targetSiteUrl))
        {

            var web = ctx.Web;
            ctx.Load(web);
            ctx.ExecuteQuery();

            var allProperties = web.AllProperties;
            allProperties["_auditlogreportstoragelocation"] = "/site/LibraryName";

            web.Update();
            ctx.ExecuteQuery();
        }
    }