I assume you're referring to Share Content Model Manager (CMM) ?
Content modeling with Model Manager | Alfresco Documentation
If you can analyse the calls from Share CMM to the Repository, you will see that Share uses a "private" CMM REST API.
You may be able to use this private API to deploy (dynamic) models that remain compatible with Share CMM ? Please be aware the API is not public, hence subject to change at any time (ie. not officially documented or supported - in terms of backwards compatibility). There are also some limitations for models supported via Share CMM, so your mileage may vary. Please run your own modelling tests (and also search JIRA).
Alternatively, you can also manage Dynamic Models via the public APIs (CMIS or REST):
Deploying a content model: dynamic approach | Alfresco Documentation
In this case, you will need to construct a valid XML content model. As an admin, this can be uploaded to the "/Data Dictionary/Models" folder and activated (by setting "cm:modelActive" property to true) - using Share &/or public APIs:
alfresco-repository/contentModel.xml at master · Alfresco/alfresco-repository · GitHub
It should be noted that dynamic model changes must be "incremental". Dynamic models can only be deleted if there are no existing references. In the future, it might be useful to support a non-incremental development mode. This would be similar to updating / removing static models (and potentially leaving residual references &/or broken behaviours that depend on the model).