how can i use my 365 microsoft word

You have the 32BIT Office 365 Applications installed on your MacBook from the past. Now you have macOS Catalina which only runs 64BIT Applications. This applies to the Office 365 Applications as well.

You will need to go to Microsoft's Office 365 Website and then sign into your Office 365 account. After that you download the 64BIT applications of MS Outlook, MS Word, MS Excel and MS PowerPoint etc. Once you complete that then all will be back to normal. Also, review the forums on Microsoft's website as well and it will guide you in the right direction.

Axel F.

You need Office 2019 or a Microsoft 365 subscription for Catalina. Older versions won’t work. If you have an active subscription, update your apps.

Else, there are free options like OpenOffice, LibreOffice or Apple’s Pages.