Prefered domain change

I am trying to figure out how to change our prefered domain on google search console. I have ran a site audit on a website called SEMRush and a number of errors have come to light that relate to duplicate content/title tags/meta descriptions. It says this is because every page on our website has 2 versions, 1 main one without www. in and another link with www. included. We would like the main link to contain www. and remove these errors.

Can anyone help?