You can use GeoGebra to complete the square of a quadratic expression, using either CAS or Algebra View.
GeoGebra Instruction 1
Algebra View or CAS under View in Menu. CompleteSquare in an empty row. Then you’ll see the following: CompleteSquare(<Quadratic Function>)
<Quadratic Function> and press Enter. CompleteSquare(<Quadratic Function>)
in CAS, you can choose to get the exact value written with fractions.