To record a VAT claim from your old system to Zoho Books, kindly follow the instructions below:
Create a new Other Current Asset account, and give it a name, say Old Input VAT. Please refer this link to know more about creating an account.
Create an opening balance for the Old Input VAT account, and enter the VAT claim amount in the debit column. Please make sure that the opening balance date should be an earlier date than all your transactions. To know more about how to create an opening balance, kindly refer this link.
Create an Expense refund for Old Input VAT account with the same amount as the recorded opening balance. Please refer this link to know more about creating an Expense refund.
and GST filing.