Search their username in Instagram
Check whether their profile appears in search results
Open any old DM conversation with them
Tap their profile from the chat
Look for a profile page with no posts, no followers, or no following
Try visiting their profile from another account
Ask a mutual friend to search their account
Check whether their comments or likes on your posts disappeared
Search their name from a web browser while logged out
If their account cannot be found from your account but appears elsewhere, you may have been blocked