Conditional calculation for duplicates in Power Query / Excel?

I have a column called “Total” that contains the total price of a product.

The issue is that sometimes the same product appears more than once (duplicate rows). When that happens, I want to apply a specific calculation so that the total is adjusted correctly for each duplicated row.

But if the product only appears once, I want to keep the original total without any changes.

Also, this table is created by merging two tables using Power Query, and it gets updated regularly whenever new data is added to the source tables.

So basically:

If there are duplicates → apply a custom calculation

If not → keep the value as is

The solution should still work correctly after every refresh

Is there a way to handle this dynamically in Power Query or Excel?

Any suggestions or approaches would really help