If you have blocked someone by mistake and now you don't know how to unblock them, then read and follow the steps given below it will help you.
- Open your profile
- Click on three horizontal lines on the top right corner and then click on settings
- Click on Privacy & then click on blocked accounts
- You will find all the blocked accounts there and then click on unblock on the account which you want to unblock
If you get any problem then read this article:- https://getassist.net/block-someone-on-instagram/