Revoke File Permissions on External HDD

My iMac broke.....

Connected to it were 3 external drives with about 6TB of media files. I connected the drives to another device and I am able to read the files on them. However I can't write, edit or delete on those drives as I don't have permission. I also can't copy and move those files to a brand new drive.

I could reformat the disks but will of course lose all my files, so my question is, how can I override the file permissions (or disk permissions) and regain full read, write, edit, delete access?

Or is there any other way I can do this.

Thanks