how can i set the default location to a sd card in sico tablet

Well it is really going to depend on which actually tablet you are using (as there are a few) and which OS that tablet is using.

First the OS. If the tablet is using anything prior to "Marshmallow", and is not upgradable to "Marshmallow", then no your device will not be able to set the SD card as the default download location. That option only comes in "Marshmallow". In which you would set a SD card to "Internal" rather than "External".

If your tablet is running "Marshmallow", or able to be upgraded to it, then you 'may' be able to do as you want. I say 'may' because the device may not allow it, that is up to the manufacturer. Some have restricted that ability, and also on the age of the device. If its hardware is to old then it would not work.

If, by some chance, you can get or have "Marshmallow" and the device is capable, then you will need a blank SD card to set to "Internal". Why blank? Because when you set it to "Internal" the device will format the card and also encrypt it to work with only that device. This will wipe any data you had on the card and will also make the card unusable with other devices without completely wiping and resetting the card, again.

Because of this, I would really suggest backing up anything you already had on the SD card prior to trying to set it as "Internal".