Currently not on packagist, so you'll just have to clone it into your project:
git clone ... whatever you can figure it out.
You must install this service provider.
// config/app.php
'providers' => [
...
SamYerkes\SiteImprove\SiteImproveServiceProvider::class,
...
];
Then you'll need to publish the config file of this package with this command:
php artisan vendor:publish --provider="SamYerkes\SiteImprove\SiteImproveServiceProvider"
$siteImprove = new SamYerkes\SiteImprove\Siteimprove;
$allSites = $siteImprove->all();
$individualSite = $siteImprove->find(1351616669);
$individualSiteAccessibilitySummary = $siteImprove->accessibilitySummary(1351616669);