From the manual, might be of use:
Viewing Charts in Multiple Monitors
Put the main Sierra Chart window in a normal state. Not a maximized or minimized state. Right click over the title bar of the main window and Select Restore to be in a normal state. Adjust the position and size of the main window to fully cover the two monitors or three monitors if you have three monitors. Open 2 or 3 charts into a chartbook. Multiple charts can be opened at the same time in Sierra Chart. Put those windows also in a normal state. Adjust the position and size of one of the windows to fill up one monitor, adjust the other to fill up the other monitor, and adjust any remaining charts you have to fill up other monitors. Select File >> Save on the menu to save the charts in a chartbook so the window positions are saved.