Adjective for the adverb "soon"

"Imminent" and "impending" should suffice.

You can also say "in a jiffy" if it's gonna be real quick. Pronto is another good, though informal, word meaning "quick".

Upcoming
adjective
up·​com·​ing | \ ˈəp-ˌkə-miŋ \

Definition of upcoming
: forthcoming, approaching

[Source: Merriam-Webster Dictionary]

'Upcoming' could work for that sentence and is commonly used in this situation. M-W gives some recent examples on the Web:

• Along with Tim, Sir Elton John and Beyoncé will also be working on the upcoming soundtrack.
  — Victoria Rodriguez, Seventeen, "Everything We Know About the Live-Action "Lion King" So Far," 10 Apr. 2019

• As royal reporter Katie Nicholl reveals in her upcoming book, Harry and Meghan: Life, Loss, and Love, Von Westenholz—a publicist for Ralph Lauren—apparently gave Harry Meghan's number.
  — Rachel Epstein, Marie Claire, "Royal Reporter Katie Nicholl Details Prince Harry and Meghan Markle's Blind Date," 8 Apr. 2019

That feature will be added in an update coming soon.

I guess coming soon would be called an adjectival phrase.