In the original manuscript, Oliver Cowdery was near the end of a line when he started to write trust. He initially wrote trut, then overwrote the incomplete second t with an s. By then he had reached the end of the line, so he inserted his correction somewhat above the line. But instead of writing just a t, he wrote ts, which forced him to cross out the extra s. The plural trusts was undoubtedly not intended, but the plural s was accidentally written because of the problem Oliver was having with the order of the s and the t at the end of trust.
The rather remote possibility that the original text could have read trusts here in Alma 57:27 makes one think of the case of mights in the Book of Mormon text. As discussed under Jacob 1:19, the original text favors the plural mights over the singular might (the singular noun is, of course, what we expect in modern English). But the case of trust is different: the noun trust occurs only in the singular in the Book of Mormon (18 times) and always in the phrase “put one’s trust in X”. Eight of these refer to more than one individual (five with “their trust”, two with “your trust”, and one with “our trust”). Thus there is no reason to suppose that in Alma 57:27 trusts, which is what Oliver initially wrote in 𝓞, actually represents the original text; it is simply the result of a scribal slip at the end of a line.
Summary: Maintain the singular trust in Alma 57:27; although Oliver Cowdery ended up writing trusts in 𝓞, he immediately corrected it to the singular trust.