We recommend purchasing a Microsoft 365 Apps for enterprise subscription so you can continue to use InfoPath. If you have a Microsoft 365 Apps for enterprise subscription, you can download and use InfoPath 2013 which is the latest version of InfoPath.
If you're running Microsoft Office on a Windows 8.1 PC, we strongly recommend you move to a supported Windows operating system to maintain the reliability and stability of Microsoft 365. See the System requirements page for more details.
Download InfoPath 2013 to work with your Microsoft 365 Apps for enterprise subscription from this location:
https://www.microsoft.com/en-us/download/details.aspx?id=48734
View help content for InfoPath on the Microsoft 365 Help & Training site.