Blackbeard for Men Instant Beard Color, Brown/Auburn, 1 Pack | 1-Day Temporary Facial Hair Tint, Beard, Mustache, Eyebrow, Sideburns, Hypoallergenic Dye Alternative, Up to 45 Applications

Have him try something like this first to see if he likes it: https://a.co/d/0jhqh6FU If he does then a semi permanent auburn hair dye every month or so should do the trick for his eyebrows.