Solution: Holy crap, that puzzle is obscure and hard. I hadn't looked at it for over a year, and could barely solve it myself. I don't know what I was thinking back then. Anyway, here's the solution...

First thing to notice is that the last line almost spells "SECURE", a synonym for "Collect". To get this word, the second S must be changed back one letter in the alphabet to an R. The cross on the left has four -1s, indicating that wherever a cross is placed, the four letters around it back up one space in the alphabet. So, the first step is to place a cross centered around the I above the second S, which changes the S to an R and changes three other letters as well.

Now, the second-to-last line spells "OCTAIN", almost the word "OBTAIN", again a synonym for "Collect". Place a cross centered on the A above the C, which will change more letters. Keep doing this, and after placing 5 crosses, the 6 lines should read:
accRue
corral
muStEr
gAther
obtaIn
secure

The capitalized bold letters show where the five crosses were placed. The crosses were centered on the five letters RSEAI, which can be unscrabled into yet another synonym for Collect -- RAISE -- the solution to this puzzle.