Yes but there are some requirements...
- AP model = AFAIK only AP39xx have iperf3 installed
- the wirless client must be able to reach the AP IP = the best is to setup a SSID with bridge@AP untagged so both are in the same subnet
Then ssh to the AP and switch in the /usr/bin directory and start the iperf server with "iperf3 -s"
Now you'd need a iperf3 app on the client and start the iperf-client to run the test.
Example below - hardware AP3915i and Amazon Fire D10
AP:
Amazon Fire HD10: