You need to configure two options to get Power BI to show your tooltip page when you hover over the visuals in your report. You will also need to define which tooltips you want to appear when you hover over a specific visual.
First, you need to turn the Tooltip slider to On, in the Page Information card, to make the page you created a tooltip (see below).
The next step is to define the fields you want the tooltip to display. Select the visuals in your report that contain the field you specify, and the tooltip will appear.
You can tell Power BI which field or fields to apply by dragging them into the Tooltip fields bucket, which you can find in the Fields section of the Visualizations pane. In the image below, the Sales Amount field has been dragged into the Tooltips fields bucket.
There can be either categorical, numerical or measures fields in the Tooltips fields bucket. When this has been done, your chosen options will automatically substitute the default Power BI tooltip.
Configure the Tooltip Manually
Alternatively, if you can find a Tooltip card in the visual’s Formatting pane, you can get the tooltip to appear when you hover over the visual. Please note: not all visuals can display tooltips.
Select the visual you want to setup. In the Visualizations pane, select the Format section and expand the Tooltip card. Select the tooltip report page you want from the dropdown for the visual.
Unfortunately, tooltips setup for custom visuals will not appear on mobile devices.