[Alan Anderson]

Put something this in your user_routine, substituting appropriately for switch_value and relay_fwd/rev:

static char relay_state = 0; /* 0 means forward, 1 means reverse */
static char last_switch_value = 1; /* will remember the last state of the switch */


if ((last_switch_value == 0) && (switch_value == 1))
{
    // here is where you toggle the relay state
    relay_state = 1-relay_state;
    if (relay_state == 0)
    {
        relay_fwd = 1;
        relay_rev = 0;
    }
    else
    {
        relay_fwd = 0;
        relay_rev = 1;
    }
}
last_switch_value = switch_value;