For your case:

docker exec -it <CONTAINER> gunzip < backup.tar.gz | pg_restore -U <USER> -F t -d <DB>

Remote restore is also available if your container is public facing and remote connections are allowed in pg_hba.conf for postresql:

gunzip < backup.tar.gz | pg_restore -U <USER> -F t -d <DB> -h <HOST_IP> -p 5432

As a rule of thumb, it is good idea to document your backup and restore commands specific to the project.

How take backup of the data which is existing in the running PostgreSQL container

1. Create some folder in your root

   mkdir -p '/myfolder/bdbackup'
   

2. download the postgres image which you are using and execute the following command

   docker run --name demo1 -e POSTGRES_PASSWORD=passowrd -v /myfolder/bdbackup:/var/lib/postgresql/data -d postgres 
   
   docker exec -it demo1 psql -U postgres
   

3. Back up will be stored in the following folder /myfolder/bdbackup

4. you can kill the container and stop the container any time but data will be stored in the host.

5. and once again re-run the postgres the container with same command

   docker run --name demo2 -e POSTGRES_PASSWORD=passowrd -v /myfolder/bdbackup:/var/lib/postgresql/data -d postgres 
   
   docker exec -it demo1 psql -U postgres
   

   and execute following query select * from emp;

6. you can see the data has restored...