You can turn off the pen writing function of U90 by the following steps:

1. Open the main interface of U90.

2. Click the "Settings" icon in the upper right corner of the screen.

3. In the pop-up setting menu, find the "pen writing" option and click it.

4. In the "pen writing" option, just turn off the "pen writing switch".

U90 is an educational electronic product. Its main functions include pen writing, AI precise learning, intelligent interaction, multimedia playing and e-book reading.