1. Obtain you Connectish API credentials (free trial available)
2. Use "Connectish Apps - HTML2PNG" action to export your image
3. The resulting image is base64-encoded PNG file - you can save in right into Bubble "image" field, but more preferably, upload it to your Bubble storage with e.g. "Base64 to File" or similar plugin
Demo editor:
https://bubble.io/page?type=page&name=html2png&id=connectish-plugins&tab=tabs-1