Assuming there's no ties in the max values in any one row,
and the source data is in cols A to J in Sheet1, from row1 down
In Sheet2
---------
Select A1:C1
Put in the formula bar and array-enter, i.e. press CTRL+SHIFT+ENTER:
=LARGE(Sheet1!$A1:$J1,{1,2,3})
Fill down as many rows as there is data in Sheet1
A1:C1 will return the 3 largest values from Sheet1's A1:J1
A2:C2 will return the 3 largest values from Sheet1's A2:J2
and so on