Remapping or tuning

Hi, I was wondering if anybody could help me. I fitted some vance and hince straight shot exhausts to my suzuki intruder M800 (VL800) but the exhaust didn't have anywhere for my lambda sensor to go so I fitted a blanking plate instead. It runs like a bag of poo now and was wondering if I maybe needed to get it remapped or tuned for the pipes. I am at my wits end with what to do to make it run better as some people tell me I can't get it remapped because the lambda sensor has been removed, some people say I can get it remapped and some say it needs retuning. Many thanks, Nikki