@Brend 

Please assign an IP address for the 2nd TL-WR841N which is different from the IP address of the main router and first access point. 

Below is the instruction to configure the router as an access point. 

https://www.tp-link.com/support/faq/417/

May it help and have a nice day. 

OK, thank you for the reply, but I'm having trouble logging into the first acces point to find the IP address of it, or is there any other way to find the IP of the first access point? 

And do I disable or enable dhcp on the second access point? 

Thanks! 

@Brend 

You can try to login to the web UI of the main router to check the IP address of the first access point.

For the second access point, to make it work, please disable the DHCP server and ensure that there is only one DHCP server existed which is the main router. 

Good day. 

If I log in to the main router web UI, I only get to see the IP of the router right? 

@Brend 

Once you logged into the web UI of the main router, first you can get the LAN IP address of main router itself.

Then you can go to DHCP client list page, there you can find the IP addresses of the devices which have been connected to the main router, including the first access point. 

Good day.