For Applications, you can find the settings used under Settings > Web and mobile monitoring > IP determination. Dynatrace uses a few widely used headers to extract the true cient IP address. However, your application may use a custom header for tracing the original client IP. You can add that header in this settings page. Alternatively, there may be a config issue where the load balancer actually strips any header that carries the original client IP and as such this behaviour needs to be corrected at the LB level.
Hope this helps.