If you want to use your X64 terminal with AS400 you will need to download and run the as400setup zip file, which you can find following the path Support > Downloads > Manufacturing and clicking on the "Software for connecting to AS400" link.

The link is the third on the page and it is shown in the image below.

you should save the zip file on your hard drive in an known location, then you should extract its contents to a folder and run the setup.exe file. A dialog box should come on the screen as shown in the image below. Click ok to proceed with the installation.

Here you can select the location where you can install the software, and to start the installation you should clink on the button with a computer station icon.

Then you should choose "As400 remote Terminal" from the list of existing groups of software on your hardware as shown in the image below. Click the button continue to proceed.

If no problems occured, you should now be able to see installation successful screen as shown below.