Your pandacoin.conf file is in your Pandacoin data folder, you can view it from your Pandacoin wallet.  Use the Settings menu then select Open Configuration File.   You should then be able to edit and save it, at the top for instance add a line reservebalance=20000 or minting=0 then save the file.

Exit and restart your Pandacoin wallet.

500 confirms are required for maturity.  There is a capability as hinted too above to reserve some balance from stake mining / minting also you can disable minting altogether by editing your pandacoin.conf

If you think you will need to spend your coins in the near future, then it is best not to mint for that time in case you solve a block and have them unavailable for a short period. It is also possible to set a “reserve balance” of coins that won’t be used for minting by using the
Set reserve amount not participating in network protection.  using an entry like   reservebalance=20000  in your .conf file