How can I use text input to copy a another cell dynamically?

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I am seeking a way to create a  rule to assist me with schedule readability. I want to enter a "B" into any cell and have the cell to automatically populate with the corresponding information contained in another column and the same row. For example: If I enter "B" into cell P5, then I want cell A5 copied into P5 instead of the "B." Then if I enter "B" into cell D36, then I want cell A36 copied into D36 instead of the "B." Etc...

Can anyone help me with this?

Thank you for your time. 

Lance

[#2]

Hello,

Excel cells can contain either a formula or a value. If you enter a value into a cell, it cannot automatically change to a formula that pulls data from somewhere else. But you can enter a value into cell P5 and then let the next column use a formula that pulls the value.

If you don't want to use that approach, you will need VBA to replace the B with the desired value. Are you happy to use VBA?