You do not celebrate this day. You should be embarrassed if you know about the Six Day War, or even words like the year 1967.

You can do one or two things to celebrate the day of Jerusalem’s unification in private. Work it the same way you would if people asked about your acquisition of a computer. Say nothing and hide it. Do not tell your children, because they talk.
Do not even mention Hallel. Praise and thanking Gd for Jewish unity are forbidden.
Point is that you shouldn’t even know the name of this day.
Any holiday that is not in the Tanach (Bible- you hedenist who probably calls it a Tanakh) is not something you celebrate, or should even know of. The only occasions we celebrate that are post Tanach are days of mourning. Mourning is mutar; Tisha BAv (Ninth of Av- you non-Hebrew speaking Apikores, who probably can’t even say it in Yiddish), The Omer, but not happy days during the Omer. You can mourn on Yom Yerushalayim, to celebrate the unification of the Jewish capital. Celebrating with a ripped shirt, while mourning the destruction of Beit Hamikdash (House of Holy- you heretic who would even think to use the word ‘Temple’ and ‘Great’ in the same phrase) is acceptable.
Even saying Tanach is shameful. I should have said, ‘Holidays mentioned in the Gemara’ (because to say Talmud shows you are an heretic- you heretic who is probably praying and thanking H’- probably pronouncing the full name Gd- for bringing us back to our Home Land).
Many non-frum Shomer Shabbat (keeping the mitzvot of Shabbat- you money laundering heathen who works on Shabbis and calls it Shabbat) Jews who believe that Israel is a blessing from H,’ make their way to the Kotel on this day. The children march to the Old City and parades happen. Parades are Asur (forbidden- you Hebrew speaking heathen who would even call it a ‘mitzad’).
As a frum Jew, the only aspect of a parade that you are allowed to join is the protest. You should be out at the protest, as this will allow you to skip school and work, and that is a mitzvah.
And to even think that you could call a day ‘a holiday’ that you can shower on?!!! Oy.