What can i do when my camera is not working showing me that the flash is disabled?

What makes you think the flash is disabled? Is it because of an icon like this:

Or this:

If the flash just generally doesn't seem to work, here's a checklist to test it:

1. Remove any case or film that might block the flash.
2. Test the LED flash by trying the flashlight in Control Center. On an iPhone X or later or an iPad, swipe down from the upper-right corner of the screen. On an iPhone 8 or earlier, swipe up from the bottom edge of any screen.
3. Tap the Flashlight button .
4. If the LED flash doesn't work as a flashlight, contact Apple Support for help with your iPhone, iPad, or iPod touch.
5. If the flash works only sometimes, open the Camera app and tap the flash button  to choose a different setting.

(from https://support.apple.com/kb/HT203040)