Atlassian’s document describes how to install apps, including Excel-like Tables for Jira:

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.

Atlassian Marketplace: https://marketplace.atlassian.com/apps/1223727/excel-like-tables-for-jira?hosting=cloud&tab=overview

Product page: https://www.ricksoft-inc.com/excel-like-tables-for-jira/