Hi @SheilaP !
There's probably different RegEx formulas you could use for this, but I found one that worked great in my demo environment. There's another for the special UK addresses but unsure if those apply to you. When you use Modify, you're going to use the Formula action. The formula / function is called RegExMatch and you're going to enter the following formula but the ${BillingPostalCode} would change depending on what field you're using:
RegExMatch( ${BillingPostalCode} , "^[A-Z]{1,2}[0-9][A-Z0-9]? ?[0-9][A-Z]{2}$") 
The other formula, which is much more complicated, accounts for "special cases."
RegExMatch( ${BillingPostalCode} , "^(([A-Z]{1,2}[0-9][A-Z0-9]?|ASCN|STHL|TDCU|BBND|[BFS]IQQ|PCRN|TKCA) ?[0-9][A-Z]{2}|BFPO ?[0-9]{1,4}|(KY[0-9]|MSR|VG|AI)[ -]?[0-9]{4}|[A-Z]{2} ?[0-9]{2}|GE ?CX|GIR ?0A{2}|SAN ?TA1)$") I cannot think of a way to fix these automatically. The above formulas will identify those fields that are not structured properly. You would then edit them manually right while you in the Dedupe preview screen or export the grid with the record IDs, fix the flagged records, and then update them using Import.
Hope this helps!
