HP 2035s like to default to A4 initially too.

If running Windows 10, press the Start button and type Control Panel. Choose the Control Panel desktop app at the top of the search results.

If running Windows 7, press Start, choose Control Panel.

Choose View Devices and Printers. Find your HP 1606 and right click it. Choose Printer Properties from the context menu. Choose the Advanced tab, then click Printing Defaults. The paper size is probably set to A4 here. Choose Letter instead and things should work better.