Thank you for reaching out to the SQL Forum.
You can download SQL Server 2016 Express for free directly from Microsoft's official site:
https://www.microsoft.com/en-us/download/details.aspx?id=56840
This edition is ideal for lightweight applications, development, and learning scenarios. Once on the page, click Download, select the installer (SQLServer2016-SSEI-Expr.exe), and follow the prompts to install.
I hope this information helps you resolve the issue.
Thanks,
Lakshmi.