Using Tableau Data Prep:

Combine the two files $($OpeningTB$.$xlsx Download OpeningTB.xlsx& ClosingTB.xlsx Download ClosingTB.xlsx$)$

Opening Debits$/$Credits Closing Debits$/$Credits

For each of the files you will need to calculate ending balances for each account $($hint: you can't use Null in a calculation$),$ see an example below of what your final data model should look like. Note how the balance for account #$1000$ is positive while the balance for account #$1001$ is negative.

Combined File