You tried zooming out the camera far away? If you set the camera distance to a very large number (far away) it should do what you want (obviously it might perform badly due to the distance but that is another issue).
If you just want to change the distance of the camera without the player zooming out, go into the data editor and click on Cameras (it's under "Edit Advanced Data" when you click on the green plus in case you don't find it). Click on "Default Camera" and double-click on the field "Initial Parameters +". Change "Distance" to a higher value. Close this window and go to "Zoom Levels +". Delete all values there. (This ensures that a player can't zoom in to the original distance when you dont want that)
If you want the player to be able to zoom out of the map, then just go to "Zoom Levels +". Click on Zoom Level 0 and copy-paste this value. Move the copied value all to the top (so it becomes Zoom Level 0) and change its distance to a higher value.