Azure DevOps Dashboards can be renamed easily provided, you have proper permissions. To rename a dashboard make sure you have a basic license and then follow the below steps.

Step1: Go to Dashboards under Azure Boards

Step2: Click on All Dashboards

Step3: Select the Dashboard you wish to rename

Step4: Click on the Gear icon (Settings) at the top right as shown in the below screenshot

Step5: Edit the name of the Dashboard as shown below

Step6: Then click on the Save button

Step7: Renamed Dashboard will be displayed with a new name as shown below