Lookup value from Power Query Dataset

Hello from a first time forum user as well as an excel "learner".

I am trying to populate a excel cell from a value stored in a data table. The data table is populated from a Power Query using the odbc.Query option.

The excel worksheet contains a GL Account details (AccountCode,Description) and then a column for each month where each column contains either the actual balances for past months or forecast balances for forward months.
Each month there is a requirement to replace the current month forecast balance with the actual balance (currently a manual task).

I have managed to extract the data from the accounts database into a data table (GLBalances) that contains columns such as AccountCode, PeriodNo, Balance.
My attempts to use combinations of VLOOKUP, INDEX and MATCH to extract the value from the data table and populate the excel cell have been unsuccessful as I cannot work out how how to reference the data table column as the source and then do a lookup using the AccountCode.

Could someone please assist - should I be able to lookup a value stored in a data table and, if so, how do I identify the data table and column (range) that contains the source data.
An example of a formula would be great.

If the above won't work, are there any suggested other options to achieve the above.

I hope the above makes sense and appreciate any assistance.