There is no best way but I can share a tip.
Exchange the Tier 4 pet with a Tier 1 Level 10 pet (Wizard Gosphy does not work) that has the desired skill you want on the Tier 4 pet.
So if you have a Cat that has learnt Gathering 5% skill at level 10 and you want your Tier 4 pet to have it, simply exchange it (Remember to choose the Cat’s skill list) and let the other skills be randomized.
Yes, you will lose two skills to RNG. But you are guaranteed to have that one skill that you desire on your Tier 4 pet now.
You can use the free pets you get from events and attendence rewards with this tip.