I had Avast Premium account and it has expired; I need to remove my gmail account from Email Guard with Avast One.
You need Avast Premium Security (even on trial) to deactivate Email Guard, see this FAQ.
How can I remove Email Guard from my email if I don’t have Avast Premium Security installed?
Maybe you can ask Avast support to deactivate it, via “CONTACT US” button from below of the FAQ.