If you are working from a version of the ArcGIS Indoors Information Model created prior to ArcGIS Pro 2.6, the ArcGIS Indoors team at Esri has created a tool to support you in updating your Indoors geodatabase schema to support the new Space Planning, Office Hoteling, and Workspace Reservation capabilities of ArcGIS Indoors.
Download the resource ZIP below and extract it to its own folder.
In ArcGIS Pro ribbon, click the Insert tab.
In the Project section, click Toolbox > Add Toolbox.
Browse to the folder mentioned in step 1. In the tools subfolder, select indoors-pro-2_6-upgrade-tools.pyt, then click OK.
The folder also contains draft documentation on how to set up new capabilities of ArcGIS Indoors. See the included 01-read-me-first.pdf to get started.