I have not used this method before and cannot vouch for the firmware or flashing software, but if you're out of options, I'd look here:
http://lgtribute.com/lg-tribute-5-ls675-firmware-download-unbrick-tutorial/
Please note that there are 2 pages to the tutorial. It's not easy to spot at first but before the "comments" section, you'll see links for page 1 and page 2. You'll need to click on page 2 to understand how to complete the process using download mode. I will say, this was a somewhat more common method of unbricking LG's back in the day (using the .dz) and I downloaded the zip to check it out and it seems to be on point with what I'd expect in terms of size and content. So proceed if you wish.