How to revert to stock ROM on HTC One M7

My HTC One M7 phone is S-OFF, has the latest firmware 7.19.401.2, and has nicely installed "ViperOne+9.0.0-fix", the recovery is TWRP 2.8.6.0. Everything works very well, except that the proximity sensor seems erratic, and when I have a call the ear seems to press different programs on the touchscreen. I would like to return to complete HTC stock ROM so that I assure myself the proximity sensor works well enough (or does not). Do I have to downgrade the firmware to be able to install the stock ROM? I have downloaded the stock ROM PN07IMG_M7_UL_L50_SENSE60_MR_HTC_Europe_7.19.401.2_Radio_4T.35.3218.16_10.33Q.1718.01L_release_421790_signed.zip but seem to be unable to install from TWRP. Or maybe the only way is via fastboot? With the commands: 1) htc_fastboot oem rebootRUU 2) htc_fastboot flash zip RUU.zip 3) htc_fastboot reboot-bootloader Can someone more experienced give some advice, please?