Please help. And I tried downgrading but it won't let me now.

I should have justs stuck with fw1.4

Hi,
What the firmware version is your Osmo with now? If it's the latest  version presently, I'm sorry that it's not allowed to downgrade right now.
If the black screen happened only after you upgrade the firmware to the latest one, please try Trigger + Record + Power switch, which will trigger the re-upgrading automatically. (Please let me know if you don't know the detail procedures)
Some other normal troubleshooting for this problem will be as below:
1) Please re-install the DJI GO App.
2) Please check the SD card inside the camera.
3) Please check if your phone is compatible with DJI GO App, we would recommend the mobile device with 2GB RAM and the ability of processing 1080p image.