If you can get it back into TWRP recovery, as @iammjones said, you can connect it to a PC. TWRPs newer versions have an option where you can connect it to a PC and you will see a folder where you can drop files from a computer.
You would then copy a known working ROM into that folder (i.e. Download folder -- if it doesnt exist, create it). Once the copy completes, disconnect the phone from the PC and then use TWRP to navigate to that folder and install the ROM.
For better help on this type of issue see the guys at XDA.
https://forum.xda-developers.com/desire-820