someone damaged my heron with a spell for 6 damage, they went in with poro bot, i pushed them out after stunning them with back off, does heron heal spell damage when showdown ends when stunned unit gets pushed back

Yes — your Heron heals all 6 spell damage when that showdown ends.

Because the poro bot entered a battlefield where your Heron was already present, opposing units were present, so a Combat was staged and the Showdown opened as a Combat Showdown (Rule 461.3). When it closes, you proceed to the remaining steps of combat, and the Resolution Step begins with a Combat Cleanup that heals all units in play (Rule 466.1.a.1) — including the Heron and the spell damage it took earlier (Rule 348.1).

It doesn't matter that the poro bot was stunned or pushed back: attackers removed mid-showdown still leave the combat ending with the heal (FAQ 1710), and if the poro bot was recalled during the Combat Cleanup itself, the heal (step 3c) happens before the recall (step 3d) anyway. The only case with no heal is a Non-Combat Showdown — i.e., moving to a battlefield with no enemy units, which never staged combat here.