This is for those who don't know Blender to well, I'll try to make this as easy to follow as possible, make sure to keep a back up just in case things go wrong!

This is also being used with Blender 2.82!

-- Importing Horns --

File > Import > FBX > Horns of choice
Make sure you are NOT in Edit Mode, you should not seeing any vertices on the model
In the list on the top right, left click the > left of Armature.001
Left Click Body.001
Ctrl Left Click Body
Hover mouse over model window, press Ctrl+J
Right click Armature.001, and Delete

The new horns are now ready to be exported!
This method also applies to the tongue model

-- Exporting the Model --

File > Export > FBX
Make sure to click Armatures under Export FBX in the bottom left hand side and uncheck Add Leafbones
Either replace an existing FBX for easier importing into Unity or set a new name, and Export FBX