1. If it is a space name signature, just click your space name directly after entering your space

There is an edit button there

, you click it. Just edit and save it

2. If you want to change the signature every time you comment or leave a message to others, click the settings button in the upper left corner of the space and in the row of "Personal Center".

(It’s the one in the middle), and then there are some settings on the left. If you choose to modify it, it will be ok. You can also set pictures. Remember to save it O(∩_∩)O~