There are two confirmed Helot revolts in history.

You need to understand that the Helots were routinely oppressed in Spartan society. Historians have described them as "serfs" and "semi-slaves". Victor Parker has pointed out that they were between slave and free as they were property of the Spartan state and could not be sold off from their land. The Helots were essentially Sparta's agricultural labour force who were used for hard labour in the fields. They had very few rights. They were settled on a piece of land and had to cultivate it. One half of that was for the state while the Helot could retain the other half. Unlike slaves, Helots' could not be removed from this land and sold at will. They could not be parted from their families/ Spartans sometimes characterised them as "enemies" and declared "war" on them annually to kill them. This was to circumvent any legal stricture against murdering helots. A secret police organization called krypteia spied on the helots and often killed the brighter and stronger members. Thus clearly the level of oppression meant that a revolt was always possible.

Historians agree that a large percentage of the Helots were made out of the people of the Messenian region who were defeated and conquered by Sparta in the 7th Century BC in the First Messenian war. Around 660 BC these conquered Helots revolted against Sparta and the ensuing conflict is known as the Second Messenian War. At this time Sparta was locked in combat with Sparta and defeated them at Hysiae in 669 BC. Sarah Pomeroy suggests that this victory helped trigger the Helot revolt. The causes for this revolt are not difficult to understand as I have already stated the condition of the Helots. But also it must be remembered that the first Messennian war and loss of Messenian liberty was in the recent past and so the subjugated people considered this to be a good opportunity for an uprising.

This Messenian revolt and the fact that the Helots outnumbered the Spartans gave rise to a recurrent Helot phobia which has been attested to by many historians. Spartans dreaded a general revolt and remained always vigilant.

In 464 BC after an earthquake devastated Sparta (contemporary sources like Diodorus estimate a 20000 strong death toll) the Helots revolted, taking advantage of the general chaos and devastation and actually established themselves on a mountain - Mt. Ithome. The Spartans struggled in laying siege to this mountain so they appealed to the Athenians for help. Parker suggests that the Spartans were inexperienced in siege warfare, preferring the straight forward combat of the battlefield while the Athenians had a better reputation with sieges. The Athenians under Cimon's leadership agreed and sent a force who also did not have any significant success and were dismissed by the Spartans. Parker points out that this could be because of the rule that Spartans had to supply the Athenian army, being the party that had invited them in the first place. This event was one of the points at which Athenian and Spartan relations began to deteriorate.

Interestingly, the Spartans were never able to totally defeat this revolt. In fact laying siege to the mountain meant keeping the Spartan army tied to the homeland which let other states like Athens and Megara have a free hand in their own foreign ambitions. Ultimately they had to negotiate with the Helots and had to let them go at around approximately 455 BC. This group of Helots were later picked up and settled in Naupactus on the Gulf of Corinth by an Athenian fleet.

It should be noted that Helots were often granted freedom or tempted with freedom to get them to participate in battles. Herodotus talks about 7 lightly armed helots supporting 1 Spartan soldier. Donald Kagan and the Cambridge Ancient History list incidents where Helots and freed Helots fought in the Greco-Persian and Peloponnesian Wars.

You can check out the primary sources like Thucydides and Plutarch.

Sources:

Sarah B Pomeroy ed. Ancient Greece: A political, social and cultural history OUP 1999.

Victor Parker, A History of Greece: 1300 to 30 BC, Blackwell 2014.

Donald Kagan, A New History of the Peloponnesian War

Cambridge Ancient History, Volumes 3,4 and 5.