Hi,
There are multiple things to check to address this issue.
One is what Eric mentioned, which is a slow server. For this one, you’ll have to contact your hosting service.
Another way to improve this is by using a caching plugin w/ proper settings. You can try Autoptimize plugin for this.
As for other issues that your site may have, you do a checklist with this article as reference:
https://onlinemediamasters.com/reduce-server-response-time-wordpress/