Keith Urban is planning to boost the American Idol finalists' success -- and remind them to listen to their gut -- when he returns to the show as a guest mentor for the Season 21 finale on Sunday night (May 21.)

"If you've made it this far, I think you're [good]," Urban tells People ahead of the big finale, where he'll be offering advice to the top three contestants: Iam Tongi, Colin Stough and Megan Danielle. At the conclusion of the show, one of those contenders will be crowned this season's winner of American Idol.

"Most artists I've ever seen at this point have a pretty good sense of what they need to work on, what they're good at and what they're not so good at," Urban goes on to explain. "I think they're open to help at this point, maybe not so much early on, but by the time you get into the top three like this, I think they're all pretty receptive to good feedback."

But Urban says that it's important for the contestants to know what kind of feedback will help them. "I think for an artist at any level, it's knowing what advice to take and what advice to discard, because it's not all accurate, no matter what somebody says," he points out.

The country star is no stranger to offering his perspective on Idol. He served as a full-time judge from Season 12 to Season 15, and earlier in the 2010s, he was also a vocal coach on the Australian version of The Voice.

On Sunday night's episode, Urban will perform "Wild Hearts" -- his high-flying anthem for following dreams -- and he says that he selected that song in part as a message of support to this season's Idol finalists.

"I chose it because I think it really lyrically suits the journey that these artists are all on," he explains, "and getting to play on that stage with my band is going to feel great."

"Now listen, has anyone ever told you you'll never amount to anything? / You're just wasting your time chasing the tail of a dragon kind of dream? / But I'm here to tell you anything can happen in this life / If you got that heart and the passion and a God-lit fire inside," Urban sings in one verse of "Wild Hearts." That's a message intended for all the dreamers out there, the singer says -- including those watching from home.

"A lot of people who watch the show have dreams and aspirations, and they're either pursuing those or they've put them on hold, and they just need a reminder to get back on that track again," he reflects. "The song is definitely an anthemic call to following your dreams, for sure."

The Season 21 finale of American Idol will air on Sunday night at 8PM ET on ABC.

Remaining 'American Idol' Contestants: Season 21

Who is left on American Idol? Here are the remaining American Idol contestants from Season 21, starting with the Top 26. This list will be edited after each round of voting.

14 'American Idol' Singers Who Secretly Hooked Up — Or Did They?

At least two couples who met through American Idol got married, while one more could be headed in that direction. Not all American Idol hookups have a happy ending, however. Here are seven of the most talked about meet-ups, plus the real scoop on how serious things got.