Here is the official firmware download information for the router.
https://www.tp-link.com/us/support/download/tl-wr850n/ tp link tl wr850n firmware download
If the above link redirects, manually navigate to: https://www.tp-link.com → Support → Downloads → Search "TL-WR850N" (Links lead to TP-Link's official servers) Here is the official firmware download information for