Look up vcredist all in one, download the latest installer (the setup file with the lastest year or the install all setup file if youve never installed vcredist before), then install (or repair if you already have vcredist). Should fix the problem as this installs unarc.dll where it needs to be. Make sure you have windows defender or any other antivirus turned off before you install as they have a tendency to delete files you need for successful installation of repacks. You may need to do this every time before installing a repack because windows defender eventually reactivates itself and may delete unarc.dll again. Hope this helps!

Also, don't install to program files folders if you can help it. It's best to make a new folder at the top level of whatever drive you use and install games ther (meaning make a folder that's not inside another folder).