ShareMeUp enables investors to grow their shareholdings by recurring investment.
However if you wish to sell your shares then you will need to contact a NZX participant broker.
A list of NZX participant brokers can be found at https://www.nzx.com/services/market-participants/find-a-participant
You can also find more information regarding some participants from within the ShareMeUp App by navigating to the "Sell" menu item.