From the Halachah Hotline of the Five Towns and the Rockaways: “One may repair previously worn clothing; e.g., replace a button, sew a tear, fix a hem, or resole shoes.”
JB2 – Halachos of the 3 weeks are different than those of the 9 days. During the 3 weeks (until Rosh Chodesh Av), you can sew and fix things, so you can take your pants to a tailor.
But, if they are your only pants, my question would be what will you wear while he is fixing them?
I too read what was sent out by the Halachah Hotline of the Five Towns and Rockaways and IMO they are stating that one can fix or alter already worn clothing, even in the 9 days.