A TS report and a Power BI Web report (see How to create a Power BI report) are linked using the IDs that identify the tenant (your company), the workspace, the dataset and the report layout. 

How to edit and find the report IDs

You can edit the reports' IDs via the Settings/"Edit" button:

The Power BI report ID is part of the Power BI Web URL:

When you view the corresponding semantic model/dataset, you will see the dataset ID in the Power BI Web URL:

Your own "My Workspace" is not identified by a unique ID visible in the Power BI Web (thus blank in TS):

All other workspaces have a unique ID:

The tenant ID is visible if you click on your profile in Power BI Web and hover above the tenant name:

How to add a Power BI report layout and link it to a TS report

You can open the dataset/semantic model connected to a report if you open a report in Power BI Web and click the "three dots":

Add and link a report layout created in Power BI Web

Start by creating a blank report:

Select visualisation and data fields:

Save the report:

Copy the report ID and paste it in TS to connect the dataset to the new report:

Save and run the report in TS:

Add and link a report layout created in Power BI Desktop

Open the semantic model in Power BI Desktop via Home/Get data:

Select the dataset/semantic model you want to use for your report layout:

Design your report layout and save it:

Publish your layout via File/Publish:

Copy the report ID and paste it in TS to connect the dataset to the new report:

Save and run the report in TS: