Firstly to begin adding a condition, create a new or edit an existing conversation. Once viewing the conversation you can drag and drop a condition from the right side menu. Once the condition is dropped into a suitable place on the timeline you will be presented with the type of condition you wish to ask in a menu on the right side of your screen.
Now select, 'Respondents' from the menu. You should now see the fields and options possible to fill in for this condition type.
The only field that needs to be filled in for this condition type is for the IDs respondents that you wish to filter your conversation with. Respondents' IDs currently can be found by exporting previous conversations and selecting the 'Add unique user id' option - you can take the respondent IDs from the exported csv file.
It is possible to manually type in the respondent IDs - one respondent ID per line, using enter to add a new line. It is also possible to copy and paste the 'user id' column from the exported csv file.
Note: Any invalid respondent IDs (respondents/IDs that don't exist) will prevent you from creating the condition.
Once this field is completed, press the pink 'Save' button at the bottom of this menu. This will add your condition into the place within the timeline where you dragged and dropped it to and affect the elements (questions, messages and other conditions) below it.