Installed pacman repo but no option to switch repos in yast (kde new install).
That is a very compact description and it does not tell us very much.
What do you do, where would you expect to see what in YaST where it isn’t?
I assume you want to do a vendor change to packman
In Yast Software management select view-repositories select packman you will see a new line at the top “Switch system packages” that will do the vendor change
From command line you can do zypper lr note the number of the packman repo say it is # then
zypper dup --from #
where # is the number of packman