How to fix this PageSpeed Insights issue?

Hi everyone,

I've been trying to get our new website to be performant and I've been using PageSpeed Insights to see where things go wrong and what could be improved.

We now have a score for mobile of 97/100, which is awesome, but I want to get the last issue as well. ;)

Problem is that I don't know how to get this fixed.

This is the issue:

Leverage browser caching

Setting an expiry date or a maximum age in the HTTP headers for static resources instructs the browser to load previously downloaded resources from local disk rather than over the network. Leverage browser caching for the following cacheable resources:

• https://www.googletagmanager.com/gtm.js?id=GTM-V5BG2 (15 minutes)
• https://js-agent.newrelic.com/nr-974.min.js (60 minutes)
• https://www.google-analytics.com/analytics.js (2 hours)

Keep in mind I'm not a server engineer or anything, but is it somehow possible to set an expiry date or maximum age on an external source? Or is there anything else I can do to get this issue solved?

Thanks in advance!