this is what i did...
when i accidentally put gain weight instead of lose weight i grabbed my two year old and weighed myself with her (she weighs 13kg) it said i reached my goal and allowed me to reset goal i put in lose maximum amount, then overwrite old body test, then do body test again and it will say you have achieved new goal and allow you to reset again and put in your new goal, hope this helps

Hehe, that's a very neat trick

I'm surprised it didn't comment on your sudden weight gain!