Anything that has to be done row by row is not going to work. It will essentially take forever.
im going to give you the Excel workflow, and you will automate this, it will be much faster.
select column B
on the Home menu, far right, left click “Go To” -> Special -> Blanks ‘now all the blank cells in column B should be highlighted and the first blank cell should be active. For the following formula, I am going to assume B2 is the first blank cell in columnB, but instead what you want to do is send keys for =Left({Right},14). So in the case of B2, you would get:
=Left(C2,14)
then send keys {Control}({LShiftKey}({Enter}))
Ctrl + Shift + Enter copied the formula to all selected cells, so to recap
Select Column B
Go to Special -> Blanks
=Left([Cell to the Right],14)
Ctrl + Shift + Enter
Done.