Enter this in A1 of Sheet
=INDIRECT("Sheet1!"&LOOKUP(ROW(),{1,2,3,4,5,6},{"A","B","C","D","E","F"}&COLUMN()))
then copy across and down...
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If you want beyond F then add to the lookup
or enter numbers in Col A of sheet3 and corresponding letter numbers in Col
B and
use VLOOKUP(Row(),Sheet3!A:B,2,false) instead of Lookup
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Use
=INDIRECT("Sheet1!"&CHAR(ROW()+64)&COLUMN())
it will work for 26 columns...