After the death of H.R. in The Flash, he reverted to the season 2 incarnation and Harry, in season 4. This lore continued until season 6, which featured a great Harrison Wells twist through Crisis on Infinite Earths.
With the destruction of the multiverse, The Flash was left alone with Nash, until the situation was found to be far more complicated than that: untold numbers of Harrison Wells survived the Crisis by merging into Nash’s consciousness.
This apparently included Reverse-Flash, but The Flash was able to exorcise it from Nash’s body. The rest, however, still exist in his mind and could presumably be used in future episodes.
One particular version of the character, H.R., may play a role in the next episode of The Flash and in the season as a whole. The season 7 premiere episode is titled “All Well Finish Wells,” which is also the title of one of H.R.
If so, he could interact heavily with Nash as one of Harrison Wells’s “ghosts,” or perhaps he could play a much larger role. An H.R. Post-Crisis could even be Harrison Wells from The Flash.
That doesn’t seem too far-fetched, as one of the first episodes of the season is when The Flash brings a new Wells. Also, reusing an existing version would be unprecedented as noted above.