If you want to use Dynamic Routes to create a destination that automatically adds the caller’s CID number to the Allow List (i.e. after caller has successfully navigated an IVR or otherwise proved themselves not to be a robocall) you can do so using this expression:
${SET(DB(allowlist/${CALLERID(number)})=Auto-${CALLERID(name)})}
This expression will not return anything useful, so you won’t be able to branch the call with this, just write it and move along to whatever the default destination is.