How to do esal e thawab?

Hadhrat Haji Mohammad Sharif khalifa of Hakim al-Umma (may Allah have mercy on them) wrote in his wasiyet (will),

“Never arrange a gathering for my esal e thawab, neither purposefully nor on ad hoc basis. Every person who desires to do so can do it individually by supplications, giving charity or performing supererogatory (nafil) worship. At the least recite sura ikhlas thrice and forward its reward. InshaAllah, this action will be very beneficial to their own selves also.”

Musaferan e akhirat, page 27