how do i iron on a patch onto a jacket?
SEW IT ON--the fabric will not tolerate heat and the ahesive will not last long. Certainly your uniform shops can sew it on. I have been a firefighter since 1964--I never saw an iron on patch.
You can go to tandy leather and use an ax all to use a specialilized needle and thread. I have a jacket 28 years old from JC Whitney with a lot of patches (leather and pre fab) that still is bad to the bone. Learn some leather craft or have a friend or have it done by someone familiar with leather work,
Lay a damp cloth over the patch then iron it. Make sure the iron is set on medium temperature. Personally I would stitch around the edge with black thread instead of ironing it. Stitching keeps all of the edge down and it won't come off as easy as an iron on patch would.
