Help me with Blessing of the Valkyrie!

Im still stuck on level 6 where it requires you to level your units 100 times.
Im wondering if from level 5 , where its requirement is 75, do i have to just level up my units 25 (increment) more times to get to the lv. 6 requirement or do i have to start all over (reset) and level up another 100 times for all my units.
I have trouble unlocking that skill since i have been leveling more than 25 times since i got lv.5, at least probably more than 50 levels and i still havent been able to learn it.
Or is there a formula or method that im missing or not understanding?
And btw, im already way past the level requirement, 54, for my account incase anyone was wondering.
Please help me with this. Thx a lot.

Just play this game longer, u will eventually unlock all skills lol

use 3 1* units to level up a 2* to level 4, then level up a few 3* units to level 10 by feeding them your 1*'s and 2*'s. This SHOULD be the fastest way to level up your units anyway, but it'll help you get that skill leveled up at the very least.

Ok, thx so much for the advice : )