Welcome to the Community. Do you mean to say how to make changes to the existing dashboard? If so,
First you have to be workspace admin to make the change
Let's say if you are a workspace admin then make sure model is not in deployed mode.
If both the conditions satisfy then
Go to Dashboards-> Edit on Top Right Corner and Dashboard designer mode will be open, you can make changes in this mode and once done save and exit. But if you wish to publish module or charts you have to go back to the module->View->Publish