Install OpenWrt on Tenda ac9

How can I install OpenWrt on my Tenda ac9. I only found one file .trx and the firmware checksum of my download matches the checksum statedn't on the download site!

See this old thread

donc si j'ai bien compris mieux vaut éviter de l'installer dessus ?

so if I understood correctly better to avoid installing it?
thank you

@Karim, welcome to the community!

Please provide English translations.