Download Stock Firmware for Sony Xperia Z5 Premium E6853 6.0.1 Marshmallow Update Firmware.
Install the Downloaded Flashtool.
After the Installation you can See the C:\Flashtool\firmwares this Folder.
Copy your Downloaded Firmware book With addendum .ftf and Paste it into the Firmware folder.
Connect Your Mobile Via USB abstracts Cable.
Ignore the Fastboot Mode Step.
Select the Flash Button with the Electric Symbol.
Select Flashmode in that.
Select the Binder as C:\Flashtool\firmwares and in your Right ancillary you can Find Wipe beat the Wipe abstracts and Wipe Cache.
Select no Final Verification and Select ok.
Follow the Instructions that Will arise on the Screen.
Wait for the Process to be Complete.After the Process Complete Turn on Your Mobile.
You can Check the Firmware Details->Settings->About->Version.