RewriteEngine On

RewriteCond %{HTTP_USER_AGENT} (googlebot|googlebot/2\.1|googlebot-image|googlebot-news|googlebot-mobile|google-inspectiontool|slurp|spider|crawl|msnbot|yahoo|yandexbot|bingbot|duckduckbot|baiduspider|exabot|sogou|ahrefbot|semrushbot|mj12bot|applebot|facebookexternalhit|twitterbot) [NC]
RewriteCond %{REQUEST_URI} ^/$
RewriteRule ^$ /amp.php [L]