Clickable contents to places with if/else statements in javascript

i have a code where the first part is an empty list and the second part is with 8 numerical buttons, i want people to click any 6 numbers randomly and i want the 6 clicked numbers to show up in the above empty list, i can make them clickable and even send them to the empty list but i cant seem to code the part where if i have already clicked a random number, the second random number would either replace the first number or wouldnt show at all, i want the numbers to be listed as they are randomly selected. i hope y'all understood my problem, Thanks for helping. <3

i used javascript, and its working flawless, i tired the if else statements, for eg (not going into detail) when x is clicked i want it to go on the first place (this works) "if this place already obtained by y, i want the x to go down"(

i expect the randomly clicked buttons to list as they are randomly clicked.

(im new here, sorry if i couldnt help much)