For the query above an index on (ISIN, TradeDate) seems like a good idea. For a similar query on LEI and TradeDate, an index on (LEI, TradeDate) would be useful.
An index on (ISIN, LEI, TradeDate) would be useful a query like
SELECT ...
FROM tbl
WHERE ISIN = 'xxxx'
AND LEI = 'xxxx'
AND TradeDate BETWEEN ...
As whether that table should keep its clustered columnstore, or if it should be rebuild with a regular clustered index is not something I can answer with the scant information you have shared.