You can't perform a CPU sampling for one Method, you have to do so for an agent.
Are you sure the Method was called since restarting the JVM?
If so, check the "Deployed Sensors" Tab in the Agent Overview Dashlet if the Sensor was correctly deployed. If that is the case and you don't see the method in the method dashlet you can start a CPU sampling for the relevant agent via: Runtime Analysis -> CPU sampling.
Select the Agent, start the sampling and then execute a transaction where the relevant method is called. Stop the sampling and open the analyzed sample, you can search for the method there.
You can find more information about CPU sampling here: https://www.dynatrace.com/support/doc/appmon/application-monitoring/dashboards/runtime-specific-dashlets/cpu-sampling-dashlet/