As per the
wiki, looks like you just connect CHR /A13 output to CIRAM /CE input, and tie CIRAM A10 input high or low (either gives you single-screen).
In your schematic, the first connection is already made. It has pads for H and V mirroring. You could add another that has an option for tying "VRAMA10" to GND, in the lower right corner.
