From Gary Chapman’s book, The 5 Languages of Appreciation in the Workplace:
Give a verbal compliment (Say, “Thanks for…”; tell them, “I’m glad you are part of the team”).
Write an email (“I just wanted to let you know…”; “it is really helpful to me when you…”).
Stop by and see how your colleague is doing. Spend a few minutes just chatting and checking in on them.
Do something with your coworkers, like eating together.