Atlassian’s document describes how to install apps, including Excel-like Tables for Jira:
Manage apps (Jira Cloud)
See Find and add new apps section for the details.
You can also add it from Atlassian Marketplace. Go to marketplace.atlassian.com and search Excel-like Tables for Jira. You will find Try it free button at the upper-right corner.
Product page: https://www.ricksoft-inc.com/excel-like-tables-for-jira/