To create a new token for your API key from Dentally, you will need to log in to Dentally and click on Settings in the bottom left.
From the next page, click on Developer
Then click Generate new token
Next, enable the below permissions
Next, copy the token provided to the clipboard or leave the window open, as once you have refreshed or clicked on another page this will no longer be available. 
Now that you have your API key, you will need to log in to Practice Admin and browse to Account and then Integration Setup Account > Integration Setup and click on Update configuration
Then click on Update API Key
And paste the API key you obtained earlier from Dentally and click Save.
Congratulations, you have now updated your API key from Dentally into your Healthengine profile. You can confirm this is up and running by refreshing the Integration Setup page after a few moments, and you should see Integration Healthy? show as Yes.
Now that it's up and running, you can go back and disable the old/previous Healthengine API key via Settings > Developer, as outlined in the first two steps and click Delete on the old key.
For more information on how to use the Dentally API, their help page can be found here.