Hi..just purchased my mavic & tried to uodatw the firmware several times using dji go apps & dji assistant..any suggestion?

You have to have a good WiFi connection for the firmware to download to your device.
On the computer what message are you getting when you attempt to update. If you can post a quick video clip that would help.

Don't use wifi, unless you have 5Ghz. Your wifi will likely hardly work due to the mavic begin 2.4Ghz and has a higher Tx-rate. Use your 4G on your phone or 5Ghz Wifi.