Enter the personal information page through WeChat My Page, open more information, and then you can change your personal signature. Let me demonstrate it with WeChat version 8.0.33.

1. After opening WeChat, click me.

2. Click on the "WeChat avatar" in the upper left corner.

3. Click on more information.

4. Click on the personalized signature.

5. Delete the original signature, enter a new signature, and click Save.

Disclaimer: This answer is original based on my real experience, and I refuse to reprint it without permission.