Permissions Errors for files on multiple external hard drives

Are you asking about changing the permissions on all the files at once?

You can Get Info on the enclosing folder and set the permissions for that, then use Apply to Enclosed from the Gear menu to propagate the change everything inside the folder.

Note that due to security changes, you may not be able to do that to the top level of the drive. You'll have to start from the first level subfolders.

If there is an Ignore Ownership checkbox in Sharing & Permissions of Get Info for the drive, checking that should give you full access, but there have been problems reported here where that doesn't work. May be worth Relaunching Finder after checking the box if it doesn't give you access.

I was hoping there was an app or terminal command line I could use and by magic it would fix the problem, but probably asking for too much.

There is, and I told you how to accomplish it in the GUI.

You can run a terminal command, but it won't do anything more than what I described to do in Get Info. If the root level of the hard drive can't be modified in the GUI, the Terminal isn't going to change things. You'll have to step down to one lower level and modify those folders and everything in them with Apply to Enclosed.