Open the homework help, click My Options in the lower right corner, and click the account avatar above. Open the profile page, and then click the identity below to open it. On the page of "Open Set Identity", select "I am a teacher" at the back. Back to the profile page, you can see that the identity is a teacher and the modification is successful. Detailed steps:

1. Open the homework help and click My Options in the lower right corner.

2. On the page that opens, click the account avatar at the top.

3. Open the profile page, and then click the identity below to open it.

4. On the "Open Set Identity" page, select "I am a teacher" at the back.

5. After selection, click Save at the bottom.

6. Back to the profile page, you can see that the identity is a teacher and the modification is successful.