Michhaammi Dukdam (Michchhami Dukkadam) is asked on the occasion of forgiveness at the end of Paryushan. In Jainism:

• For Shwetambar Jains: the last day of Paryushan is called Samvatsari. This is when people greet others with Michchhami Dukkadam and seek forgiveness.
• For Digambar Jains: the same day is observed as Kshama Vaani (forgiveness day), also the time to offer Michchhami Dukkadam.

So, you typically wish Michchhami Dukkadam on Samvatsari (the last day of Paryushan), to reconcile and forgive any hurt you may have caused, and to ask for forgiveness from everyone you may have wronged.

If you’d like, I can share the exact dates for Samvatsari in a specific year.