picklist_data.json
Open the file picklist_data.json, located at picklist folder, as shown below:

add a new data item as shown below:

<picklistname>.picklist
this file is located at ../Artifacts/picklist folder:

add the new line item as shown below:

<picklist name>.dml
this file is located under ../WEB-INF/classes/types/dml/picklists folder:

add the new line, as shown below:

<picklist>.json
this file is located under /classes/types/json/picklists folder:

add a new block for that item as shown below:

application.properties
this file is located under: D:\tomcat-9.0.85-8000-XCP\webapps\<appname>\locales. and add the new line item as shown below:

Steps:
- stop tomcat service

- delete the work folder

- clear tomcat document / cache folder (this is important)

- start tomcat service
you will see the new item into the dropdown list.
