How to use serial port to show the RAM and modify the RAM start value in macOS?

[zhong]

I want to add a new ble service in hrs example(sdk15.3),I build and run the hrs example.and then I open the terminal emulator, but I can't find anything.I try to click the option"connect /dev/tty/usbserial",but makes nothing.How can I get something like this?(

<warning> nrf_sdh_ble: Insufficient RAM allocated for the SoftDevice.

<warning> nrf_sdh_ble: Change the RAM start location from 0x20002B90 to 0x20002B98.

<warning> nrf_sdh_ble: Maximum RAM size for application is 0xD468.

<error> nrf_sdh_ble: sd_ble_enable() returned NRF_ERROR_NO_MEM.) 

because if I don't change the RAM, I won't find any service by bluetooth.

[zhong]

the details is in this problem:https://devzone.nordicsemi.com/f/nordic-q-a/46061/using-nrf52840-to-try-to-add-dfu-service-in-the-hrs-example-failed-sdk15-3-0

I don't know how to success in adding dfu buttonless service in another app,this problem shows how to change ram if I add another ble service