WIFI does not work on Lenovo Ideapad 120s (Ubuntu 18.04)

Question

I took apart the computer to upgrade some hardware, but afterwards I cannot connect to wifi.

OS: Ubuntu 18.04

CPU: Intel Celeron N3350

Output of nmcli device show

> GENERAL.DEVICE:                         lo
> 
> GENERAL.TYPE:                           loopback
> 
> GENERAL.HWADDR:                         00:00:00:00:00:00
> 
> GENERAL.MTU:                            65536
> 
> GENERAL.STATE:                          10 (unmanaged)
> 
> GENERAL.CONNECTION:                     --
> 
> GENERAL.CON-PATH:                       --
> 
> IP4.ADDRESS[1]:                         127.0.0.1/8
> 
> IP4.GATEWAY:                            --
> 
> IP6.ADDRESS[1]:                         ::1/128
> 
> IP6.GATEWAY:                            --

output of lspci -nnk | grep 0280 -A3

02:00.0 Network controller [0280]: Realtek Semiconductor Co., Ltd. RTL8821CE 802.11ac PCIe Wireless Network Adapter [10ec:c821]
Subsystem: Lenovo RTL8821CE 802.11ac PCIe Wireless Network Adapter [17aa:c024]