Md Nowfel Mahmud Bhuyian, I think it would be good to contact DLR and inquire. Have you already tried the 'proposal web forms for the higher resolution DEM products (12m & 30m DEM product) at': https://tandemx-science.dlr.de
Md Nowfel Mahmud Bhuyian , This is a 30-m dem product that is provided free of charge. It doesn't have many missing values in higher altitude mountain areas. You can download it at paragraph 4. of the following url: https://www.eorc.jaxa.jp/ALOS/en/aw3d30/index.htm