what phone do you have? there is no android 13 clock. it is whatever clock your phone carrier uses or you can download a clock from the play store. i think google has one.
on my samsung z fold 4, i use samsung's included clock app. so my path is launch the clock app>find the three dots at the top right corner>select settings>select sound>change the tune you would like to play when either the alarm goes off or the timer. your path might be differnt than mine. basically go into the clock settings and look to change the sound.