Add the celery to the pot of your pressure cooker. Place the chicken tenders on top of the celery. Add the chicken broth and lemongrass and lock on the Instant Pot lid.
Cook on high pressure for 22 minutes and use the quick release to let off the steam.
Use tongs to remove the lemongrass and discard.
Pour in the coconut milk and give the soup a good stir. Season with salt and pepper, to taste.
Serve with cooked rice or cauliflower rice, fresh lime, and sliced scallions, if desired.