I am new to trading options and use ameritrade. My first option trade last week was to sell a DEC 18 $25 CALL option (1 contract) on RNVC. The underlying security is currently trading over 25 so the option is in the money. I do own 100 shares of RNVC which I purchased at $24, so i guess this is what's a covered call, although I did not purchase as a covered call on ameritrade, but rather purchased the shares and sold the option contract separately. Now that the option is in the money my understanding is that it can be exercised at any time. How do I make delivery of the shares if the option holder chooses to exercise it?