Sometimes camera might not work for some glitches and it can be easily fixed by restarting your phone. I had the same problem with my new [link|https://technosamigos.com/blu-f91/|BLU F91 5G mobile|new_window=true] but it's now fixed.
Please do it and that's easy.
If it doesn't fix the problem then you will have to [link|https://blucellphones.us/factory-reset-blu-phone/|reset your BLU phone|new_window=true], that's the only option left.
Still the issue is not fixed then please contact BLU if the phone is under warranty.
Finally if it's not under warranty then you can't do anything except replacing the camera module or chip.
The best thing would be to get a new phone instead of BLU Studio 7.0 II