Get root access inside mssql docker container

I created a MSSQL docker container based on the official image provided by Microsoft (https://hub.docker.com/_/microsoft-mssql-server).

I started a bash shell inside the running container and tried to delete some files.

sudo docker exec -it sql1 "bash"

Inside the container it is using the mssql account (by default).

And there seems to be some permission issues when I tried to delete the files.

rm -f *.csv
rm: cannot remove 'xxx.csv': Operation not permitted

How can I obtain the root permission to delete the file? I am not sure what default password I can use to run rm as root.

Thanks a lot!

Source: StackOverflow