Who should do the job? Excel or Prime.
Whoever should do it has to be able to access the full table to be able to find the column with the desired header text.
If Excel should do the job, you could provide the desired column name as input in the Excel component and use the methods available in Excel to find the desired value and write it in a specific cell which then is returned to Prime.
If Prime should do the job, you would have to read in the whole table in a Prime variable and use Primes lookup or match functions to find the appropriate value.
Find attached a sheet which shows both methods (both with an embedded Excel component). I found the first one not being reliable as it would not always update correctly.
Personally I would prefer omitting the Excel component and reading in the table from an external sheet via READEXCEL.
But both, component and READEXCEl have their pros and cons. Using READEXCEL you would have to handle two files instead of just one.

Attached file is in format Prime 9