most abilities I've seen that are like this, say something like
"grants fly speed 30 (average) or +10 if you already have a fly speed"
So, by the RAW you wouldn't gain any benefit from said ability if you don't actually possess a fly speed. Think of it this way, if something said "increase your damage with swords by 3" it wouldn't actually do anything for you unless you had a sword and it certainly wouldn't cause you to spontaneously gain a sword that does 3 dmg.
What ability are you seeing this language on?