You can install the Beautiful Maps - Mapbox plugin by going to the 'Plugins' tab of your Bubble editor and searching for 'Beautiful Maps - Mapbox'.
You can either buy a lifetime licence or subscribe to the plugin on a monthly basis.
Bubble plugin subscriptions are pro-rated. This means you can try the plugin out and if you un-install it after a few hours it will cost less than 10 cents!
Alternatively, you can purchase the plugin from the plugin page, choose which application you'd like to install it in and then click 'open editor'.