To add a new option on a dropdown menu within SIMS e.g. behavior activity type or medical condition go to:

Tools > Lookups > Maintain

Press the Search button, this will list all the lookups available to change

Double click on the Lookup, and the press the New button, when making a new value, double check the 'active' box is ticked

A log out of SIMS is required for the changes to be updated