Pick what each button should do. The complete Karabiner rule set assembles below, scoped to this mouse alone. It opens preloaded with the current configuration, so you are editing a working set rather than starting empty. Each button can carry a second action on hold, and any two side buttons can be chorded. Nothing leaves this page.
B4 and B5 are the left flank, live from the factory. B6 and B7 are the right flank and send nothing until you assign them in Ultimate Software.
Red marks anything your current selection changes — the wheel press included, though it is black on the mouse itself.
Manual diagram pieces 2, 6, 7, 8, 9
Loaded with the configuration the repository ships with — Back, Delete, forward-delete on Ctrl, and Return on the wheel. Change any of it; Buttons 6 and 7 start unassigned.
Two side buttons pressed together, giving a gesture neither has on its own. Chord rules are emitted first — placed after their own buttons' rules they would never fire, because Karabiner takes the first match. The wheel press is not offered here: mixing a pointing button into a simultaneous rule is untested on this hardware.
Paste into Karabiner-Elements → Complex Modifications →
Add your own rule, clearing the default contents first.