Here is my guide how you straighten your beard in a two step process. The first step will naturally straighten your beard to give a more natural look, whereas the second version will give you straight hair like you might see on top of your head.
To straighten the beard in the first stage you'll need beard oil, styling product, and a hair dryer with attachments. I will blow dry my beard up and out on a low speed at medium heat. The faster the speed and the higher the heat, the straighter your beard will be.
Once the beard hairs have been separated, I'll use the focusing hair dryer attachment to blow the side of my cheeks down. For me this helps them look thicker because I have thinner cheeks.
For stage two, you'll need a mini straightener and some hair clips. Clip away sections of your beard so that you have an easier time accessing sections of hair. From there with one slow, gentle swoop - start from the roots and go to the edge of the hair with the straightening iron. Continue until beard is straightened to your preference.