The Yealink SIP-T41S and SIP-T42S require a specific firmware version to work with the DD10K DECT dongle.

The firmware for that model can be found at Yealink's download site under Wireless IP Phone > W41P.

Update the firmware then attach the DD10K dongle.  You may be prompted to update the dongle firmware. Allow that and then when complete reboot the phone for pairing with the DECT base.