Firstly make sure option widget for instagram is enable.
After that you must get User ID and Instagram Access Token
Since 1 June 2016 instagram change term of service developers to access instagram API. There are need to regenerate your instagram access token. You must change option instagram access token value with new token. Before you generate token and instagram ID,please update your theme.
1. Generate your instagram token here a Get Instagram New Token
2. A Also if you don’t have instagram ID go to this link Get Instagram ID
* Make sure your Account match for an instagram token and instagram ID.
Then Follow Next Step Copy your User ID and Access Token.
Fill it into tumblr options ‘Instagram User ID’ and ‘Instagram Access Token’, don’t forget to save it .