Which three Heroic Couplets from "An Essay on Criticism" by Pope achieve a satirical effect?
I take it you are refering to the Heroic Couplets in the Sixth Course of Holt's Elements of Literature, which are taken from Pope's "An Essay on Criticism." I have changed the question accordingly. Let us remember that Pope is a master of satire, which is ridiculing various aspects or institutions of society with the hope of thereby promoting change. Key tools used in satire are exaggeration and irony, but often if we look at the Heroic Couplets your question refers to, we can see that Pope's satire functions far more subtlely. Consider, for example, the following couplet:
Music resembles poetry: in each
Are nameless graces which no methods teach,
And which a master hand alone can reach.
There is of course here the implied criticism of those who try to write poetry without having the "master hand," and write doggrel as a result. In the same way, we can see a similar irony at work in the following couplet which gives some very wise advice:
Be not the first by whom the new are tried,
Nor yet the last to lay the old aside.
The balanced advice clearly indicates the dangers of being so swift to adopt a new trend that you become a subject of ridicule, but also the equal problem of clinging on to the old for so long that you are likewise ridiculed, but for different reasons.
Lastly, consider what Pope has to say about education:
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring.
To only learn a little is actually very dangerous. Therefore in our learning we must "drink deep" and make sure we learn a lot, implicitly criticising those who feel they possess deep knowledge when in fact they know very little at all.
In these couplets, therefore, Pope seems to be pointing out the various misdemeanours of humans as a race, establishing the ways in which they are arrogant, ignorant and suffer from doubt and error.