efficiently timorous twin dimensional array c#

what an fit proceed tremble twin dimensional array smaller distance c#?

for example:

var bigarray = new object[100, 100];
var smallarray = new object[10, 10];

bigarray[0, 0] = 1;
bigarray[0, 1] = 2;
...
bigarray[99, 99] = 100000;


startrowindex = 0;
startcolumnindex = 0;
endrowindex = 9;
endcolumnindex = 9;

smallarray = bigarray.someshirnkingmethod(startrowindex, startcolumnindex, endrowindex, endcolumnindex);

how someshrinkingmethod() ?

thanks!

edit: i'm simply perplexing initial 10 rows columns bigarray smallarray nonetheless i'm certain looping by array many fit method.