You need to submit request for F&O segment activation.
Go to "MY Account", then "Manage Account" & request for F&O segment activation. You need to e sign & submit income proof. Then Fyers team will activate it in next 48 hours.
PL remember that trading in F&O is highly risky & one should go for it only after getting consistent return from cash market for at least one year. Otherwise there are max chances that Trader will lose his entire capital. Be careful.