DUBLIN—Ryanair on Thursday vowed to repay customers within five days for cancelled flights in a renewed customer service push after criticism about how it handled refunds at the height of the COVID-19 pandemic. The budget airline, Europe’s largest, said refunds would be processed into a new online wallet function within 24 hours of a flight being cancelled, allowing customers to book new flights immediately or opt to get the funds back within five working days. Ryanair was one of a number of airlines criticised during the pandemic for resisting issuing cash refunds to people who could not take their flights due to COVID-19 restrictions, which the airlines said were outside of their control. Some customers also complained of delays to refunds for cancelled flights and unwieldy refund request processes. Britain’s competition authority in June launched enforcement action against Ryanair over a failure to offer refunds rather than rebooking to passengers …