How do I block a user in the main Wireless Network but allow the same in Guest Network (TP-Link ) or vice versa?

I have TP Link Wireless Router TL-WR840N (2.4GHz).
Answers

Adrian

Correct, guest network has a separate password, no need to give that person the main WPA2/Wifi password, just the guest password. If they have the main wifi password, you have to change it sorry to say....

David

Change the password of the main network