Want to only allow on my WAN port

[Smoothrunnings]

I have an SFTP server in my environment and a NAT rule setup to allow all traffic hitting port 22 on my firewall into my SFTP server. I want to know how to setup my NAT rule properly to only allow traffic into port 22 that I specify.

At work we have clients who need SFTP servers in their environments, and we only allow traffic in from specific IP addresses on both their Cisco ASA firewalls and in the SFTP software itself.

I would like to do that here. I have setup an alias and tried on the rule but after testing and having someone I know test it from his connection it just didn't work so I suspect I was doing something wrong in the setup.

Thanks,