Clicking on cell that auto fills an X and removes all other auto fills in a range

I would like a little help.

I have the following code that allows me to click on a cells in a certain ranges and it places and "X" in the cell.

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I would like it so that when I click on say C11, it would clear any other "X"s in the Range B11:E11 but would leave the other two ranges B13:D13 and B15:D15 alone. Same would hold true if I clicked D13 it would clear any other from B13:C13, but leave any "X"s in B11:E11 and B15:D15.

Any help would be appreciated.