Greetings to you.
Would you please explain how the Jews are to know when they are to return to Israel.
Jews have always believed that first the messiah will come and afterwards all the Jews will return to the Holy Land. They will go there under the messiah's leadership. See Isaiah Chapter 11 which begins with a description of the messiah, and then says (v. 12), "And He (i.e. G-d) will lift up a banner to the nations, and He will gather in the scattered of Israel, and the diaspora of Yehudah He will gather from the four corners of the earth." See also Rambam Melachim 11:1, "The king messiah will eventually arise and restore the kingship of the house of David to its former status, build the Temple and gather in the exiles of Israel."
See also the Talmud (Kesubos 111a) which states that nowadays the Jewish people is forbidden under oath to take over the Holy Land. Clearly then, taking over Eretz Yisroel is something we cannot do on our own, before the messiah comes. We must wait for the messiah to tell us in the name of G-d that the exile is over and the oath is no longer in force.
How will we know who the messiah is? He will bring all Jews to repent and fulfill the laws of the Torah (Rambam, Melachim 11:4). This is such a hard task that no false messiah will be able to accomplish it and fool the world. Whoever does this clearly has G-d's help and is designated by G-d to be the messiah.
The Satmar Rav notes (Vayoel Moshe Chapters 48 and 80) that by making the repentance of the entire Jewish people the criterion for the messiah, the Rambam is not leaving open the door for impostors. On the contrary, to make everything dependent on miracles and wonders would be dangerous, because sometimes a false prophet is given the ability to fool people with miracles (Devarim 13:3). But to make all Jews do teshuva is such a monumental task that, in the normal way of the world, no one can do it. If someone does succeed, it is a clear sign that G-d has sent him.
Whatever the criteria are for the messiah, it is clear that we have to wait for him, and thus it is certainly wrong to conquer the Holy Land under a movement such as Zionism that does not even claim that any particular person is the messiah.
Furthermore, when the messiah does come, all nations will recognize him as the messiah and there will be no war of conquest, as the prophet Isaiah says, “And it will come to pass at the end of days, that the mountain of the house of G-d will be established at the head of all mountains, and it will be higher than hills, and the nations will stream to it. And many nations will go, and they will say, come let us go up to the mountain of G-d, to the house of the G-d of Jacob, and let Him teach us His ways, and let us go in His paths, for from Zion will come forth Torah, and the word of G-d from Jerusalem. And he will judge between the nations, and rebuke many peoples, and they will beat their swords into plowshares, and their spears into pruning hooks. Nation shall not lift up sword against nation, nor will they learn war anymore” (Isaiah 2:2-4).
Thank you for your interest.