How to add camera brand or model in exif meta? In my android mobile there is no  camera brand or model in exif meta  but rest of the exif tags are ok. how can i fix this?

Model :Xstreamer Aiki 5
You can use apps like EXIF Tag Editor (Photo) and Pixelgarde to view/edit EXIF data of your images. Both apps has the ability to batch-process the images.

If you are looking for a way to automatically add information (particularly the camera model as in your question), you cannot do anything rather than waiting for an update from your device manufacturer. This is because embedding that information is configured the the ROM itself.