Modifying table

So I have a table which is populated by a CSV file which is uploaded locally, Now all the columns in table are mapped according to csv headers, however i have a column which is boolean called as lead exists which should be changed according to result of a sql query,
Basically the sql query checks if an email of lead exists and if it returns a array of 0 length, the lead exists column should be changed to false automatically within the table component itself,
Is there any way to access these table components i can also change the leadExists column to string . Any help is appreciated thanks a lot .

I'm assuming this value isn't stored in the CSV and just needs to be calculated on the go.

first, you need to add a new column for Lead Exists. just click the + to the right of the Column header:

the properties window should update and you should have the new column shown. just change the Value to something similar to below.

let me know if I misunderstood something