Welcome
Please search the forum 
I'm not sure if this is the latest version of @ptillisch's instruction but give it a try: Can't set com-state on a cheap nano clone - #6 by ptillisch
Which version of the IDE are you using?
PS
This issue only happens with (some) clone Nanos. They usually use the "old bootloader" option in tools → processor so that is also something that you need to change; I don't expect it to solve the problem.