Get a vessel with 1-2 litres of water. Add some Gangajal, a little tumeric, honey, sugar, saffron and milk. Keep a second vessel to do the Tarpans into.
Start the ritual in the same way as you would usually start your Mantra Japa session, honouring the Guru, Lord Ganesh, and meditating / contemplating upon Shri Bagalamukhi and carrying out Nyasas, Pancapuja etc.
Say something to the effect of: “Oh Bagalamukhi, I am carrying out Tarpanam to the best of my ability for your pleasure as part of my Purascharan. Please accept my worship”.
Then carry out the Tarpans. This is done by dipping the right hand into the mixture and taking some of the mixture into the right parm from the vessel, and letting it run from the palm to the fingers into the second vessel while chanting the mantra followed by “Tarpayami”.
E.g. if you are doing Purascharan of the mantra “Hlrim”, then each time you do a Tarpan, chant “Hlrim Tarpayami”.
This is to be repeated for 1% of the total number of mantras chanted for the Anushtan. If 125,000 mantras were chanted, 1,250 Tarpans should be offered. This can be done over one or more sessions (for longer mantras it would probably require more than one session).
At the end of each session, ask for forgiveness for any mistakes made in the ritual. Ask Bagalamukhi to accept your worship, infantile though it may be as a Mother would accept a child taking his/her first steps.
Please note – this is a procedure I have used. I am putting it up in case it would help someone and also to preserve it for myself to re-use in the future.
Baglamukhi, Purascharan, Anushtan, Anushthan, Bagala, Bagla, Tarpana, Tantra
Hindu Perspective 
Thx for sharing
Greeat read