It is simply impossible to change the font size in the schematic view. If it is possible then it is a well-hidden and thus a poor UX design.
I suggest you do something about it. example below.
![image.png](//image.easyeda.com/pullimage/E3ltpPqDDuHGd87MdyF19ek6btKsd3Lt2TEUjU7C.png)
Chrome
78.0.3904.70
Windows
10
EasyEDA
6.2.46