How to deal with debtor mismatch on moving from paper accounts to Clearbooks

I am moving a sole trader from paper accounting to Clearbooks. The sole trader wishes to continue with cash accounting and is VAT registered. I have entered all data (invoices / bank statements) into Clearbooks to begin on 6 April 2019. This involved entering some invoices from the financial year 2018-2019 as they were not paid until the year 2019-2020. This resulted in a trade debtors figure of c. £40,000 However, the problem I have is that the paper accounts balance sheet as at 5 Apr 2019 has a debtor value of zero. What is the solution? I cannot get the opening balances to work unless I can clear that £40,000 debtor value from Clearbooks? Do I do to reduce the Clearbooks debtor value to zero on the 5th April 2019 and presumably back to £40,000 the following day? I wish the invoice dates were all 6th April 2019 now but cannot change these because a VAT return has been submitted from Clearbooks for QTR ending 31 Oct 19 and also, some part payments were paid on the invoices in the year 2018-2019. Any advice gratefully appreciated.