if you are sure do once reset settings. and once long press on camera icon >app info>storage >clear cache >restart your device then try if after all done not worked visit service centre I told you that not supported in videos as per my little knowledge so to make sure do that things
Open camera, switch to video mode. Then switch to front camera for video. Then open settings. Auto HDR or HDR rich tone whichever option you see. Open it and then you will see option of HDR video for front camera if it is supported by your mobile.