Hi there! I understand you're facing an issue when trying to set OceanHero Browser as your main search engine—specifically, it says it cannot download. Let me help you get this sorted out.

To get started, could you clarify a bit? Are you trying to set OceanHero as your default search engine within the OceanHero Browser itself, or are you attempting this in another browser on your Windows 10 device? Also, when you say "cannot download," is there an error message, or does the process just fail without much detail?

This will help me guide you better. In the meantime, here is a general step-by-step you can try to resolve this:

1. Check Internet Connection: Ensure your Windows 10 system is connected to a stable internet connection; sometimes this error happens due to network issues.

2. Clear Browser Cache: Cached data might interfere with changing settings. Go to your browser settings, clear cache and cookies, then restart the browser.

3. Manual Search Engine Addition:
- Open the browser's settings.
- Find the "Search engine" section.
- If OceanHero isn’t listed, try adding it manually:
- Go to oceanhero.today and copy the search URL format (usually something like https://oceanhero.today/?q=%s)
- Use the option to "Add a new search engine" and input these details.
- Set OceanHero as default afterward.

4. Check for Browser Updates: Ensure your OceanHero Browser app or the browser where you are trying to set OceanHero is updated to the latest version.

5. Restart Your Device: Sometimes a simple reboot can refresh any hung processes.

If these steps don’t resolve the issue, you might be running into a permissions problem or a temporary server or hosting issue related to OceanHero's servers. In that case, we might need to check for any outages or further details from OceanHero’s support.

Let me know what you’ve tried so far or if you can provide the exact error message or situation details. I’m here to help!