I'm afraid there is no way to open a dashbaord in Model A using a button in Model B.
One thing you can try to do instead is to pull the relevant data from Model A to Model B, and reflect it in the dahsbaord (in Model B) that would have the same layout as your existing dashabord (from Model A). That way every time you press a button you would load the latest data.
Obvs what we really need is ability to construct dashboards which contain content from views across models!
But as a workaround with open dashboard button would you like existing browser tab to show different model with requested dashboard open and would have to go back (and lose state existing model at moment)? or open new browser tab leaving other tab as is? or even open dashboard from remote model in floating window as per detached tab? and if it wasnt dockable would that matter??
You could use the MAKELINK function to create a link that can be published like a button to open up the model where the other dashboard sits (make the dashboard the default to that it opens up when the model opens). Do this each dashboard in both models so that you can click to go back and forth. To use this, create a module with only a line item for each link you want. Format to Text. The formula could be similar to this: MAKELINK("Click Here", "https://core237.anaplan.com/anaplan/framework.jsp?selectedWorkspaceId=#########&selectedModelId=XXXX...")
When finished, publish the line item to the dashboard.
One consideration with this is that the core you will be assigned will likely change, meaning a permanent, hard-coded link with https://us2a.app.anaplan.com/core10112/.... etc. could be quite risky - what do you think?
I think as a feature request this would be helpful, as well as being able to create dashboards that pull data from views across multiple models. This would mean for example, you could have Workforce planning and P&L impact on the same Dashboard, without the need for duplication.