if the part numbers are always the same, except for the 'F', use a subreport...if you are using a stored proc, you find it then and add it as a column. You could also use a Command object and select all the parts that are like '%F' and the part w/o F and link them in the report, then you could just access the field w/o the subreport.
A command like this should work:
SELECT partNo, LEFT(partNo, LEN(partNo)-1) AS linkPartNo, Yield FROM tableName WHERE partNo LIKE '%F'
Then you can join the command to your table link the partNo from the table to the linkPartNo in the command, and your yield will be available. If you want to see the parts ending in F on the report, you will want to change the link type to either a Left or Right Outer Join...you will need to experiment as I am not sure how CR determines left and right.
HTH