I used to have winrar on my computer but after removing it I noticed all my .rar files have no icons. I used Dopus to open them since I never create them. Right now they are just blank white squares. When I check the "open with" in properties it shows Windows Shell Common
Any idea how to get the icon back? Or how to change it?
In Opus, go to Settings > File Types and expand the System File Types part of the list.
Check if there is already a RAR type (RAR in the Extension column. The Description column doesn't matter.)
If the RAR type exists already, double-click it to edit it. If it doesn't exist, click the New button below the list and create it.
From there you can set the icon at the top of the dialog which opens to edit the individual types.
That will usually work, unless something is overriding the type (e.g. the Open With menu can override it). If the icon is currently blank/generic then you shouldn't have to worry about that.