@Pooja321
guizero is not provided in the OpenSTLinux distribution nor is available as a Yocto recipe. As a consequence, you need to install it by yourself.
I don't know this tool so you can test this command from your board:
root@stm32mp1:~# pip3 install guizero
If the command fails beause of some missing packages, try to resolve the dependencies by installing the required packages.
If guizero needs a toolchain or relies on unavailable packages, you need to use the Distribution Package and create a yocto recipe. If you are not familiar with Yocto and Distribution Package, please take a look at the following article: https://wiki.st.com/stm32mpu/wiki/STM32MP1_Distribution_Package
To create python3 yocto recipe, you can install on your host machine the utility tool pipoe and use it to create your recipe.
Best regards
--JM
