If you don't know how to downgrade, my instructions below should be helpful.
1.) Backup your data. 2.) Review your Outlook Profiles to make sure you have all of your email account information and passwords for those accounts as you will probably have to add them in again after you downgrade. 3.) Export out any calendars, contacts, tasks, notes attached to an OST file. 4.) Have your Microsoft Store account information, email and password ready. 5.) Uninstall your current Office 365 subscription. 6.) Reboot computer. 7.) Log into your Microsoft Store account http://www.microsoftstore.com. 8.) Click on “Digital Content” (it should be at your main screen, far right). 9.) Then click on "install" the orange button. 10,)Click on “Language and install options.” 11.) Click on "Additional install options." 12.) Other versions of Office, select "Version Office 2013 32-bit." 13.) A download will start and installation will begin.
You might notice that your Outlook 2016 profile may be replaced with Outlook 2013. If you launch Outlook you may have everything back as it was or you may have to start from scratch. This is why I remind you in the first steps to have everything backed up.