Scale Blessing — ruling 1

Bolster itself doesn't target any creature, though some spells and abilities that bolster may have other effects that target creatures. For example, you could put counters on a creature with protection from white with Aven Tactician's bolster ability.

Scale Blessing — ruling 2

You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves. That could be the creature with the bolster ability, if it's still under your control and has the least toughness.

Scale Blessing : règles, fonctionnement et interactions (MTG)

Scale Blessing is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Bolster 1, then put a +1/+1 counter on each creature you control with a +1/+1 counter on it. (To bolster 1, choose a creature with the least toughness among creatures you control and put a +1/+1 counter on it.)

How it works : Scale Blessing

Original English text — Wizards of the Coast / Scryfall

#1February 25, 2015· Wizards of the Coast
Bolster itself doesn't target any creature, though some spells and abilities that bolster may have other effects that target creatures. For example, you could put counters on a creature with protection from white with Aven Tactician's bolster ability.
No other card is named in this ruling.
#2February 25, 2015· Wizards of the Coast
You determine which creature to put counters on as the spell or ability that instructs you to bolster resolves. That could be the creature with the bolster ability, if it's still under your control and has the least toughness.
No other card is named in this ruling.