Assuming you are using Win10 and trying to print by WiFi:

You first need to go to the Win10 Network settings. Finder should show up as a network, and you'll need to connect to it.

Once connected, when you select Print File in Flash Forge, you should see a pop up box that is titled Connect Machine.

Select the IP Address option.

You should see the printers IP address then (something like 10.10.100.254 8899) and then select the green button titled Connect Machine.

The file should then start streaming to the printer.

Hope it helps...