Need more detail to give a better answer.
Sorry I it wasn't much help. Can you post a link to the pattern (or give one or two of the repeating rows in the pattern), what is the guage (stitches per inch and rows per inch), count in foundation chain, and how much you need to reduce the size (in inches). The more details you can give the better answer you are likely to get.
If the difference is small, then you can try one size smaller hook to see if that gives you a better fit. You jcould make two swatches, first one using the guage of the pattern and that is at least 4 inches wide and 4 inches long and includes at least two repeats of the pattern(s). Then the second swatch using a smaller hook but the same number of stitches and rows as the first swatch. Compare the size difference and multiply it out for the number of stitches in the pattern to see if it will size it down enough or too much.
Master of Crochet, apprentice of Knit
OTN another Black & gold Diagonal Square Potholder
OTH Baby blanket
OTH Lace doily - A vintage pattern recreating from an heirloom.