Thank you for posting here in the Community, @Rajdeep.
I want to help you with your question about adding an account type. However, I need more details about it to provide the right information and to get this sorted out promptly.
If you're referring to adding a new account type in the Chart of Accounts, the option to do so is unavailable (see screenshot below). For now, I recommend choosing the closest account and detail type available in the system.
You can check out the description section to determine if you're selecting the right one. Please see additional screenshot on this: