Replacing a null value with a value fetched from a different row based off a third column

Hey cal_hallum 

You can achieve this using Power Query in the Power BI Desktop. Try the script bellow.
If this post helps, please mark as solved.
Regards,
Marcel

Script Power Query

let
// Replace the line below with your current data source
Source = YourCurrentTable,

// Custom function to look up the corresponding REFERRAL_CONTRACTS_CODE value
CustomFunction = (referralCode) =>
let
correspondingRow = Table.SelectRows(Source, each [REFERRAL_CODE] = referralCode),
result = if Table.IsEmpty(correspondingRow) then null else correspondingRow{0}[REFERRAL_CONTRACTS_CODE]
in
result,

// Add a custom column with the desired values
#"Added Custom" = Table.AddColumn(Source, "New_REFERRAL_CONTRACTS_CODE", each CustomFunction([BASE_REFERRAL_CODE]))
in
#"Added Custom"