Hi @Madhavi_G
You can click the "fx" button to set any of the table buttons to be dynamic:
You could set it to only show when the table query has data:
When downloading, you have two native options:
1) Download raw data OFF: will only download the visible columns, will include any custom columns and custom mappers you've set on your table
2) Download raw data ON: will download all database columns even if they're hidden on the table, will not include any custom columns or custom mappers from the table settings
That said, you can't currently rename the file when using the native download button 
The best way to implement naming the file yourself, is to use a custom button on the table, as we're chatting about here. Unfortunately, you can only have one custom button per table. Maybe you could have a button component next to the table if you need the custom button described above, as well as a custom download solution