I want to drag and drop my main branches anywhere on my mind map

To freely drag and drop your main branches anywhere on your mindmap, you will need to turn off Auto-layout.

To turn off Auto-Layout you need to go to open the Properties panel.

Step 1:  Go to View > Panels > Properties.

Drag and drop free hand auto-layout

Step 2: Once the properties panel is open click on the background of your mind map and then go to the Properties panel and click on the Branches tab.

Drag and drop free hand auto-layout 2

Step 3: Here you will see an option for Auto-Layout. Uncheck this option and you will be able to drag and drop your branches anywhere on your mind map.