We have configured an M-Files object so it grabs data from a Salesforce database.
How can we make it so end users can add values to this object and add this value not only on M-Files but on the Salesforce database as well?
Do you mean update properties which are read from Salesforce to M-Files so that the updated values are written to Salesforce, or add completely new properties to these Salesforce objects in M-Files?
The former should be possible if you are using the official M-Files plugin for Salesforce CRM and have set the UPDATE (and possibly also INSERT INTO) statements into the object type settings. See chapters 3.4 and 3.5 in the installation guide: Installing and Configuring M-Files Plugin for Salesforce CRM
The latter isn't directly possible as far as I know. There might be ways to achieve this with custom integration, however I'm not a Salesforce expert.