TP-Link Archer C20 V4 (US) - How Can I Enable 5GHz wireless

Hi guys
I installed openwrt on my Archer C20 V4(US) and configured it
I want to use both wireless band 2.4GHz and 5GHz!! Already enabled 2.4GHz but it's not stable,My mobile phones are disconnected sometimes :roll_eyes::unamused:
1.How Can I Fix 2.4GHz band to be stable !!?
2.How Can I Enable 5GHz !!?
Thanks for your help guys :pray::pray::v:

Any Suggestion?!! :roll_eyes::unamused::pensive: