Support to enable cache on a WordPress instance

Have created instance , installed wordpress, uploaded all data etc. to AWS lightsail. Everything is working as expected except cache. We are able to add page cache plugin to wordpress. Below is the message of one critical issue. need help to resolve it.
"1 critical issue
Critical issues are items that may have a high impact on your sites performance or security, and resolving these issues should be prioritized.


Page cache is not detected and the server response time is slow
Performance
Page cache enhances the speed and performance of your site by saving and serving static pages instead of calling for a page every time a user visits.

Page cache is detected by looking for an active page cache plugin as well as making three requests to the homepage and looking for one or more of the following HTTP client caching response headers:

cache-control, expires, age, last-modified, etag, x-cache-enabled, x-cache-disabled, x-srcache-store-status, x-srcache-fetch-status.
Median server response time was 848 milliseconds. It should be less than the recommended 600 milliseconds threshold.
No client caching response headers were detected.
A page cache plugin was not detected.