Help with Invoice format

I am unable to customise Invoice in the attached format pls help!
Any suggestion will be appreciated!

you can use any of the themes available on the website Free Accounting Software | Manager
check the guides section how to install and change a theme.
as per your screenshot you can customize the theme if you know html. you can search the forum for ideas or else you can hire someone locally to customize it for you.

I cant customise the Custom value field and it is not reflecting the changes as I save to theme !

First, this is not a software coding forum. It is a forum on how to use the Manager application for accounting, not document design.

Second, if you do not have the skills to perform the Liquid programming necessary to customize themes, hire a local programmer as @sharpdrivetek suggested.

Third, have you read the Guide about implementing the Indian GST scheme?