Account correlation not working


I have created a custom identity attribute and used a transform for its value then I made it searchable to use it in correlation configuration in source>import data>correlation. I have given that value which is exactly same as the account attribute I have done aggregation but only 2 accounts got correlated remaining didn’t . How do I solve this. Is there any API used to manually correlate them or check.

Did you perform an unoptimized aggregation on the source once the correlation attributes were changed?