Ranger Beast Master’s attack bonus

The Ranger companion says to add your proficiency bonus to the animals attack roll. Does this replace the animals proficiency bonus or add to it?

Ie does a 5th level ranger flying snake get +9 bonus or +7? The snakes natural +6 is it’s +4 dex bonus and it’s +2 proficiency bonus so does the ranger replace the +2 with her +3 bonus or add her +3 to the +6?

The players hand book says not to add your proficiency more than once which might suggest the +7 but technically the snakes proficiency and your proficiency are not the same bonus which would suggest the +9.