First off, you have "Tampered" because you actually FLASHED a recovery, which is not necessary in anyway, shape, or form... If you have read deeper and done some research than you would learn that Tampered comes from flashing custom recovery and is completely normal but unnecessary, using "fastboot boot recovery.img" when needed prevents the Tampered flag and eliminates the need for separate flashing of boot.img files when flashing custom ROMS.
There is no need to FLASH any recovery, once a recovery is flashed TAMPERED will always be there until you lock and RUU, even flashing stock recovery back will not remove the flag. Remember that "Tampered" doesn't really do anything, it is just a flag that says you have modified the phone and if you sent it in for warranty replacement, they could potentially reject it and charge you full retail if the flag is set. Tampered by itself is not an issue. Although seeings as you have already flashed a custom recovery, flashing the new one is acceptable, just remember if you flash a custom ROM that you must extract the boot.img file and flash it manually from the PC as well.Do you mean open a command prompt and type something similar to this except use twrp recovery?
Fastboot flash recovery ..\recovery-ra-vigor-3.14-gnm.img
This is the method I used to put Amon Ra recovery on my phone.