First, you sketch the normal/usual parabola x^2 - 5x + 4.
Then you find the part of this parabola, which is located in the lower half of the coordinate plane below x-axis.
This part is between the roots of the given quadratic function, whose roots are 4 and 1.
Next, you reflect this part of the parabola about x-axis, considering x-axis as a mirror.
Another way is to use automatic/electronic plotting tool/tools from the Internet.
For example, from this link
www.desmos.com
or from other similar sites.
Then the only need is to write the formula of the function in the assigned window, and the tool will make all the rest work for you,
plotting a graph is seconds. A benefit is that you do not need to think.