Answer: The Gemara (Nedarim 23b) writes that if one doesn’t want their nedarim, vows, to endure throughout the year, they should proclaim on Rosh Hashana that they wish them to be annulled. According to the Ran (Nedarim 23b), this is the source for saying kol nidrei on Yom Kippur.
According to the Mishna Berura (619:2), kol nidrei does not automatically annul all vows, however. Likewise, the Shaarei Teshuva (581:1) quotes various poskim explaining why one should specifically perform hataras nedarim on erev Rosh Hashana, while it is still Elul (See Kaf Hachaim OC 581:12; 19; Minchas Yitzchak 9:61). The Chayei Adam (138:8) stresses the importance of performing hataras nedarim at this time, writing that people erroneously view it as another prayer. Rather, people should study the halachos of nedarim, and say it in their own language if necessary so that they understand the process.
The Rema (YD 228:2) and Shulchan Aruch (YD 228:46) write that one may annul multiple vows simultaneously and annul a few people’s nedarim together, though they should use the plural refrain ‘mutarim lachem, it is permitted for you’.
While the Mateh Ephraim (581:49) writes that this should only be relied on under extenuating circumstances, the Ben Ish Chai (Re’eh 2:25) implies that it ideal for people to do it together.
R’ Ephraim Greenblatt (Rivevos Ephraim 8:533), notes, however, that if the three dayanim don’t use the plural refrain, then it is ineffective.
In conclusion, while there is a preference to do hataras nedarim by oneself, there is a precedent for shuls to do it in groups to ensure that everyone stays to do it.