GET Model Folder Id :
curl -X GET "http://localhost:8080/alfresco/api/-default-/public/alfresco/versions/1/nodes/-root-/children?relativePath=Data%20Dictionary&skipCount=0&maxItems=100&alf_ticket=TICKET_f5cff7c76f7a87139f24dc0c6540dd1b57479552"
From the response grab the "id" which is the nodeRef id of Models folder.
2- Use the upload api to upload the model file into Data Dictionary/Models folder:
Upload model xml to Data Dictionary/Models:
curl -X POST -F firstname.lastname@example.org http://localhost:8080/alfresco/api/-default-/public/alfresco/versions/1/nodes/a9a9f477-5c57-11dc-ad6c-5136d620963c/children?alf_ticket=TICKET_f5cff7c76f7a87139f24dc0c6540dd1b57479552
3- Activate the model, grab the node id of the model xml from the upload response (see highligted in the url below):