To complete the square, you need to add or substract a number that makes the expression become a perfect square trinomial.
In this case, it is necessary to add 3 to both sides of the expression, this way:
[tex]\begin{gathered} x^2-4x+1+3=3 \\ x^2-4x+4=3 \end{gathered}[/tex]Now, factor the expression:
[tex](x-2)^2=3[/tex](That is the appropiate form).
Now, solve the expression for x:
[tex]\begin{gathered} (x-2)^2=3 \\ x-2=\sqrt[]{3} \\ x=\sqrt[]{3}+2 \end{gathered}[/tex]