Could you please clarify what you mean by “aathi”?

In Jain context, you may mean one of these:

• Ayambil – a Jain tapa involving simple, bland food once a day.
• Atthai – fasting for 8 days.
• Atham – fasting/observance connected with the 8th tithi.

If you want to inform others, you could write:

“Jai Jinendra. I would like to inform everyone that I am doing Atthai/Ayambil. Please bless me with Michhami Dukkadam and good wishes for my tapa.”

Please confirm which tapa you mean, and I can help you write a proper message.