How to install OpenWrt on Comfast CF-AC50 gateway?

how to flash it under openwrt?
it is not in the list of supported devices on the site, but the router itself is defined in the network connection as an openwrt router, but the firmware is not original but Chinese and it is not possible to get higher than 135 Mbit per download on it, although the ports are gigabit, and the aggregation of the speeds of two providers. Updating the firmware from off-site did not solve these problems.

Hardware Specification:
CPU: MT7621A;
DDR: 512MB
Flash :32MB.
Physical interface:310/100/1000Mbps LAN /WAN Port. 110/100/1000Mbps WAN Port. 110/100/1000Mbps LAN Port.
DC Power Port. Button : 1Reset Button. 1Power ON/OFF Button. Power : 12V/1A. Indicator:Power,SYS

Short answer, you probably can't, not without adopting the openwrt fw 1st.

installed the latest firmware version CF-AC50-V2.6.1, download speed did not increase

screen as in the network environment, the Chinese firmware is displayed as openwrt

They all are, but it doesn't say anything about the actual conversionability from stock fw, to real openwrt.
Even completely unsupported/able devices run Openwrt.