Texas Instruments TI-83 PLUS - Manual (Page 266)

TI-83 Plus Matrices 263
2. Press | , } , ~ , and † to move the cursor to the matrix element you
want to change.
3. Switch to editing context by pressing Í , ‘ , or an entry key.
4. Change the value of the matrix element using the editing-context
keys described below. You may enter an expression, which is
evaluated when you leave editing context.
Note: You can press ‘ Í to restore the value at the rectangular
cursor if you make a mistake.
5. Press Í , } , or † to move to another element.