Row and column adjacency really isn’t a thing with AppSheet, so best to reconsider your requirement. It sounds to me that you want the initial value of some column–let’s call it ColumnA–to come from a different column–ColumnB–of the previous most-recently-added row. Set the Initial value expression for ColumnA to something like this:
([_ROWNUMBER] = MAX(MyTable[_ROWNUMBER]))
[_ROWNUMBER] refers to a row’s number in the spreadsheet. Assuming the rows in your spreadsheet are added in chronological order, oldest at the top and newest at the bottom, the newest row will have the highest row number.
MyTable with the name of your table) gives a list of row numbers in your table.