Change cell value from 0 to 1 with button

I need to change a cell value from 0 to 1 using some form of user interaction such as a button or other method.

Application Detail:
Column A - Numbered 0 or 1 representing used or unused
Column B - Sequential Numbers 0-199999
I have a VLookup function returning the first number in the sequence that has a 0 adjacent to it.
I also have a Match function returning the row number that the VLookup result is in.
I need to add a button or other interface that will write a value of 1 to Ax (where x is the result of the Match function) when pressed.

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