A creature's training ability triggers only when both that creature and a creature with greater power are declared as attackers. Increasing a creature's power after attackers are declared won't cause a training ability to trigger.

Once a creature's training ability has triggered, destroying the other attacking creature or reducing its power won't stop the creature with training from getting a +1/+1 counter.

Warrior's Resolve's last ability checks at the moment it would trigger to see if any creatures you currently control with one or more +1/+1 counters on them attacked this turn. If none did, the ability won't trigger at all. It doesn't matter if the creatures had +1/+1 counters on them when they attacked.