Input to the game is performed by manually editing the contents of RAM address 1. Using the QFTASM interpreter, this means performing direct writes to address 1. Look for "Direct write to RAM" on the interpreter's page. Each move only requires editing a single bit of RAM, and this input register is automatically cleared after the input event has been read.
1 counterclockwise rotation
4 down (soft drop)
16 clockwise rotation
If you do CTRL+F on the following:
Direct write to RAM
You can find the input field :)