Use a target that gives off heat, because plain paper barely shows on a thermal. RIX thermal targets are self-heating pads with adhesive on the back. Stick one on a cardboard box or target frame and it puts a 6 x 6 cm heat spot right where you want your point of aim.
Hang a heated target at your zero distance, fire a group, then move the reticle to the center of the group in the scope's zero menu and confirm with another group. You can do this day or night, since a thermal reads heat in daylight too. These RIX pads stay warm long enough for plenty of sight-in time.
RIX makes thermal imaging optics and the gear that goes with them. Alongside these heated zeroing targets, we carry RIX thermal riflescopes, Titan and STRIDE monoculars, mounts, lens caps and eyecups. If you're sighting in a RIX scope, a few of these targets belong in the same range bag.