Do something simple with a creator who matches or compliments your niche. For instance, fitness and nutrition go hand-in-hand. This helps you get exposure to new accounts!
You could try a live Q&A (because Insta loves lives) which notifies followers of both your account and theirs – a double whammy. Another way is to collaborate on a post together that would be entertaining or educational to your audience. This could be a “fake competition” for banter or genuine advice on how to improve squats – that kinda thing.
Top tip: Instagram’s feature allows you to collab and tag other creators easily. This means your post will feature on their feed too (if they accept).