wezterm/docs/config/lua/keyassignment/ActivateLastTab.md

ActivateLastTab

Since: 20210404-112810-b63a949d

Activate the previously active tab. If there is none, it will do nothing.

return {
  leader = { key = 'a', mods = 'CTRL' },
  keys = {
    -- CTRL-a, followed by CTRL-o will switch back to the last active tab
    {
      key = 'o',
      mods = 'LEADER|CTRL',
      action = wezterm.action.ActivateLastTab,
    },
  },
}

See ActivateTab for a way to activate a tab based on its position/index.