Dear Rafia Hasan,
Thank you for posting in Microsoft Community. We are happy to help you.
To understand the exact scenario, may I know if you made some drawings from the Draw tab, however, the Eraser option is disabled because it's grayed out? Could you please provide some screenshots about the issue?
By the way, does it work if you try adding the Eraser option to your Quick Access Toolbar?
go to File > Options > Quick Access Toolbar > choose commands from All Commands, find the Eraser command and add it to Quick access toolbar, click OK. It will show as below, does it work if you use it to erase ink drawn on page?

If it still doesn't work, please also provide a screenshot of your Word App version. I will test further to help you troubleshoot the issue. Please navigate to File > Account, then capture a full screenshot of Product Information from the Account page.
We look forward to hearing from you; Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution.
Thanks for your cooperation and understanding.
Sincerely,
Tina | Microsoft Community Moderator