Check out example codes for "kill all ports mac". It will help you in understanding the concepts better.

Code Example 1

lsof -n -i TCP:8080
COMMAND   PID   USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node     54762   user   23u  IPv4 XXXXXXXXX      0t0  TCP 127.0.0.1:http-alt (LISTEN)
PID // is second field in the response . Then, kill that process:

kill -9 54762 // here put PID number found on the table 54762

Code Example 2

sudo lsof -i tcp:3000

Code Example 3

sudo lsof -i :3000

Code Example 4

kill -9 <PID>

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