As I said before, the method will depend entirely on what mechanism
you have in place to communicate between the mainframe and the PC.
There are a number  of different products that provide that
functionality and each would have their own protocols that need to be
used. You would be best off referring to the documentation for that
product.

When I implemented this for our systems, we had two different methods
available to us.

No one will be able to help you unless you can specify things like:

-- What kind of mainframe you're getting the data  from
-- What kind of PC/servers you have
-- What communication protocols are in place
-- How your system  programmers installed the communication software
-- What security firewalls and other options they have decided to go with

...etc, etc

You'd be best off contacting your own system programmers. They should
have those details and be able to tell you how to do what you need to
do. *IF* you can at all!