They can be pretty tight at times. Just use a small wood or plastic block as a buffer to gently tap on the band, alternating sides as you go. Don’t try to move either side to much at a time. Sometimes it really helps to lightly wax the wood in front of the band along with a couple of drops of wd40 right on the wood / band seam to reduce friction. Ones really stuck can be encouraged to move by applying heat with a hair dryer / heat gun to the band. You want to only heat the band, which can be done by wrapping the surrounding areas with towels or preferably welders blankets. The old method was to use one of the large soldering irons pressed against the band but not many of us still have those. When reassembling, it’s a VERY good idea to use a small dab of lock tite or nail polish to keep those band screws from rattling loose.