First make sure that you have been blocked. This is how you can do that

Check if the profile of that person, last seen time, WhatsApp status is visible or invisible. If you can't see anything then it means you have been blocked.
The second option is to send a message to that person. If it shows only a single click, it means that the message has been delivered but has not been checked.

Know how to unblock yourself on WhatsApp

- Open WhatsApp
- Go to Setting
- Click on Account
- Select delete account option
- Enter your name and delete your account permanently
- Now, uninstall WhatsApp Messenger from your phone
- Restart your phone
- Now again re-install your WhatsApp on your phone, follow all the procedures
- Done! You have unblocked yourself from your friend's WhatsApp account.

  Hope it helps.

 2.How to unblock yourself when someone blocked you

Step 1: Write down the number of the person who blocked you and delete them from your contact list.
Step 2: Make a backup of all your WhatsApp contacts
Step 3: Delete your WhatsApp account
Step 4: Clear your WhatsApp data and uninstall it from your phone
Step 5: Go to Google Play Store and download the app again
Step 6: Register your number and restore your chats
Step 7: Add back the contact that blocked you
You have successfully unblocked yourself on WhatsApp.