In 2017 return there was a line to describe unusual medical situations, i need to add this to 2018 return. how can i do this?

Never heard of such a thing ... on the Sch A the total of medical expenses are entered as ONE amount ... the program has many categories in the interview but they are ONLY for your use only ... so you can skip all those categories and make one entry for the total medical expenses. 

on line 11 of medical expenses worksheet, you can enter descriptions for  medical items, but such info doesn't get transmitted to the IRS.   there is no need to enter any detail for medical expenses. only the total gets transmitted to IRS  

Are you asking about a state tax return?