Hi Sugana Karki,
Firstly, you need to enable the Turn on new meetings in the settings by clicking on your profile image in Teams and select Settings. Then restart Teams app.
After you’ve enabled the new meeting experience, you will be able to use the Large Gallery View in your meeting. When there are more than 10 participants in a meeting, only then you will get the ‘Large Gallery’ option in the meeting option. Large gallery view (preview) is where you can see video of up to 49 people in a meeting simultaneously.
For more information please see:
If you followed the above steps but still got the issue, please kindly capture an issue screenshot and your Teams version number to us for further analysis.
Regards,
Grace