CHICAGO—United Airlines Holdings on Tuesday reported a smaller quarterly loss than a year ago, but a resurgence in coronavirus cases slowed bookings and drove up cancellations, upending the carrier’s plan to return to profit. Chief Executive Scott Kirby, however, said recent headwinds the airline has faced are “turning to tailwinds.” United said it expects revenue in the current quarter to recover to up to 75 percent of 2019 levels, improving from about 68 percent in the quarter through September. The company’s shares rose about 2 percent to $47.22 in extended trading. Buoyed by a strong summer travel season, United was expecting to be profitable in the third and fourth quarters. It lowered its estimates last month, citing the impact of the fast-spreading Delta variant of the coronavirus on travel. Rival Delta Air Lines last week said domestic consumer travel has returned to pre-pandemic levels. U.S. carriers are eyeing a strong …