Can I replace the start/stop battery myself or does the BMS need resetting at a garage?

Thanks Les -? 

Saying it as it is, the only clue you give us is that it’s a stop/start battery, and regrettably you have chosen/can’t be bothered to, either give your name, model of car or your location. 
As one of the other moderators often says ‘ we are a friendly and helpful group’, and indeed we are,  but….. help yourself to gain the help you need! Rant over, except a please or thank you wouldn’t’ go amiss. 
Answer - almost certainly yes. 

Thanks Les. 

It'll definitely need to be coded. 

Apologies. It seems I have frightened our Les away!